Age he started: Age 7 (1988)
Then: He got his first major TV role on ABC's 1991 "Dark Shadows" series before starring on NBC's short-lived "The Powers That Be." Then, of course, was his stint on "Roseanne" before landing a lead on "3rd Rock From the Sun," which lasted six seasons and launched his career.
Now: JGL is a major movie star, headlining hits like "(500) Days of Summer," "Inception," "Looper" and "The Dark Knight Rises."
Age she started: Age 10 (1981)
Then: Applegate got her start guest-starring role on TV, with one short-lived series under her belt before landing her big break on "Married ... With Children," which brought young men 11 seasons full of Kelly Bundy antics to drool over.
Now: Even though she still dabbles in movies ("Anchorman" sequel, anyone?), Applegate is staying loyal to her TV roots, currently starring on NBC's sophomore sitcom "Up All Night" after her Golden Globe-nominated roles on "Jesse" and "Samantha Who?"
Age she started: Age 12 (1987)
Then: Before her name was synonymous with "Blossom," Bialik was the title character in a failed sitcom, Fox's "Molloy," co-starring Jennifer Aniston. She also did stints on "MacGyver," "Webster" and "The Facts of Life."
Now: After stepping out of the spotlight to raise a family, Bialik returned to her TV comedy roots with arcs on "Curb Your Enthusiasm" and "The Secret Life of the American Teenager" before joining the cast of CBS's "The Big Bang Theory."
Age she started: 12 (1994)
Then: Biel's breakout role was also one of her first, as the eldest Camden daughter on The WB's hit "7th Heaven," which ran for 11 seasons.
Now: Mrs. Justin Timberlake has continued her career on the big screen with recent roles in "Hitchcock," "Total Recall" and celeb-packed ensemble hits "Valentine's Day" and "New Year's Eve."
Age she started: 9 years old (1989)
Then: Chlumsky's first major role came when she was just 11 years old, but it was a memorable one. She played Vada Margaret Sultenfuss, the precocious daughter of a funeral home owner, in the hit coming-of-age movie "My Girl" and its sequel.
Now: She took a break from acting to go to college and start a family, but returned to Hollywood and soon got a part in Armando Iannucci's "In the Loop," a role that led to her now-starring role in HBO's political satire series "Veep" alongside Julia Louis-Dreyfus.
Age she started: Age 11 (1990)
Then: At just 14, "My So-Called Life" made Danes a household name, a role model for angsty teen girls everywhere and an Emmy nominee and a Golden Globe winner.
Now: Danes has since added two more Golden Globes and two more Emmys to her awards collection -- one each for portraying Temple Grandin in HBO's movie of the same name, and the latest for her current role on Showtime's hit sophomore drama "Homeland."
Age he started: Age 16 (1990)
Then: DiCaprio's first big role was on NBC's short-lived soap "Santa Barbara," but that landed him steady TV work on shows like "Parenthood" (NBC's 1990 iteration) and a memorable role on "Growing Pains."
Now: One of the highest paid actors in Hollywood, DiCaprio has played everyone from a modern-day Romeo to Howard Hughes and J. Edgar Hoover, and has worked with every major director, including Christopher Nolan, Quentin Tarantino and Martin Scorsese.
Age she started: Age 9 (1984)
Then: Fergie -- then known as Stacy Ferguson -- sang and danced on TV each week as herself for several seasons on "Kids Incorporated." The show launched her music career with girl group Wild Orchid.
Now: After leaving Wild Orchid, Fergie shot to superstardom as the leading lady of the Black Eyed Peas, and has since launched a successful solo career and an animated voiceover career as well (she's done several voices for Fox's "The Cleveland Show").
Age he started: Age 12 (1987)
Then: Galecki started off his acting career with several TV movies and a few short-lived series, but it was his roles in 1989's "Christmas Vacation" and the latter seasons of"Roseanne" that really put him on the map.
Now: His starring role as Leonard Hofstadter on CBS's "The Big Bang Theory" has taken his career to the next level. He even played "himself" on a few episodes of HBO's insider Hollywood series "Entourage."
Age she started: Age 6 (1983)
Then: At only 15, Gellar starred in teen TV soap "Swans Crossing" before being cast as Erica Kane's daughter Kendall on "All My Children." She eventually won her career-making title role on The WB's "Buffy the Vampire Slayer."
Now: After marrying Freddie Prinze Jr., her costar from "I Know What You Did Last Summer" and the "Scooby Doo" franchise, they welcomed their second child together just as her return to TV on The CW's short-lived "Ringer" was coming to an end.
Age he started: Age 15 (1988)
Then: After receiving a Golden Globe nomination for his very first role -- co-starring with Whoopi Goldberg in "Clara's Heart" -- Harris landed the title role on "Doogie Howser, M.D." playing the teen doctor for four seasons and earning another Golden Globe nomination.
Now: With several more TV series, movies and a cult-favorite sing-along blog under his belt, Harris can be seen as the ultimate bro Barney Stinson every week on CBS's hit sitcom "How I Met Your Mother," now in its eighth season.
Age she started: Age 10 (1989)
Then: Another singer-slash-actress who got her start on "Kids Incorporated," Hewitt showed off her pipes on the big screen alongside Lauryn Hill and Whoopi Goldberg in "Sister Act 2" before landing the role on The WB's hit drama "Party of Five," which made her a household name.
Now: Even though her "Po5" spinoff failed, Hewitt's teen movie roles ("I Know What You Did Last Summer," "Can't Hardly Wait") kept her working consistently. After five years as the lead in CBS's "Ghost Whisperer," a Lifetime TV movie "The Client List" was a big enough hit to become her latest TV series role.
Age he started: Age 18 months (1956)
Then: Howard started early and worked consistently before landing a career-making role as Opie Taylor on"The Andy Griffith Show" for eight seasons, starting at the age of 6. Tack on 10 more TV years to his resume in another iconic role -- playing Richie Cunningham on "Happy Days" -- and you've got proof that sometimes big-time success can strike twice for one child actor.
Now: He was and will be the voice of "Arrested Development," but it's his work behind the camera that's most notable now, having produced TV shows and movies, as well as directing big screen hits from "Splash" to "Parenthood," "The DaVinci Code" to "Frost/Nixon" and the upcoming Jay-Z documentary.
Age he started: Age 13 (1991)
Then: A role in all three "Mighty Ducks" movies made Jackson a pre-teen heartthrob early on in his career, which led to roles in the requisite teen movies ("Apt Pupil," "Urban Legend," "The Skulls") and a hit teen TV soap with The WB's "Dawson's Creek," which ran for six seasons.
Now: Jackson is currently wrapping up the fifth and final season of his starring role on Fox's sci-fi drama "Fringe."
Age she started: Age 12 (1995)
Then: After several TV guest spots and a guest arc on "7th Heaven," Kunis landed a lead role on "That '70s Show," which ran for eight seasons. Her distinctive voice can also be heard on "Family Guy" each week -- she's Peter and Lois Griffin's awkward daughter Meg.
Now: Kunis is now a major movie star, playing everything from the romantic comedy female lead ("Ted," "Friends With Benefits") to more dramatic roles (her memorable "Black Swan" part won her nominations from both the Golden Globes and the SAG Awards).
Age she started: Age 5 (1990)
Then: Majorino started her career acting with some pretty big names on ABC's "Camp Wilder" before breaking hearts on the big screen with emotional dramatic roles in movies like "When A Man Loves A Woman" and "Corinna, Corinna." She transitioned to more mature fare as she grew up, with a part on cult-favorite series "Veronica Mars."
Now: A role in "Napoleon Dynamite" (and the eventual short-lived animated series spinoff on Fox) led to stints on "Big Love," "Bones" and "True Blood" before Majorino joined the cast of ABC's long-running hit "Grey's Anatomy" as a new intern this season.
Age she started: Age 8 (1980)
Then: Though her career started in the theater, it was her role as Samantha Micelli, the daughter of Tony Danza's character on "Who's The Boss," that really put Milano on the map. In 1985, she played Arnold Schwarzenegger's daughter in "Commando" and her later roles -- Jennifer Mancini on "Melrose Place" and Phoebe Halliwell on "Charmed" -- secured her longevity.
Now: As well as recent appearances in the movies "Hall Pass," "New Year's Eve" and the Lifetime telefilm "Sundays at Tiffany's," Milano will play the lead in ABC's midseason drama "Mistresses."
Age she started: Age 11 months (1990)
Then: Panettiere began appearing in commercials from 11 months old, but in 1994, she landed the role of Sarah Roberts on the soap "One Life To Live," and followed it as "Guiding Light's" Lizzie Spaulding. She has worked consistently ever since. Though she had a notable guest stint on the final season of "Ally McBeal," her role as Claire Bennet in NBC's "Heroes" is her most recognizable to date.
Now: As a singer, voice-over artist and actress, 23-year-old Panettiere has appeared in numerous films, video games and TV shows, and is currently starring in ABC's "Nashville" alongside Connie Britton.
Age she started: Age 12 (1977)
Then: After playing "Annie" on Broadway, Parker's first TV role came in 1982, when she scored the lead part in CBS's "Square Pegs." The show only lasted a season, but Parker soon leveraged that visibility into features, appearing in "Footloose," "Girls Just Wanna Have Fun" and "Flight of the Navigator" in the late '80s.
Now: Parker is best known for portraying the lovelorn Carrie Bradshaw in the "Sex and the City" series (and subsequent movie sequels), and currently has a guest role on "Glee" in addition to her movie work.
Age she started: Age 9 (2001)
Then: Roberts -- the niece of Julia Roberts -- made her movie debut in Ted Demme's "Blow," appearing as the daughter of Johnny Depp's character. In 2004, she starred as the lead in Nickelodeon's teen series "Unfabulous," which ran until 2007.
Now: Now a bona fide film star, Roberts has starred in films as diverse as "Valentine's Day," "Nancy Drew," "It's Kind of a Funny Story" "Scream 4" and "Celeste and Jesse Forever."
Age he started: Age 9 (1986)
Then: Savage first appeared on television on the show "Morningstar/Eveningstar" before he was 10, but it was his role as the grandson in the movie "The Princess Bride" that really launched his career. Savage followed that up with the starring role as Kevin Arnold on "The Wonder Years" from 1988-1993.
Now: As an actor, Savage has recently appeared in shows such as "Happy Endings" and "Family Guy," and has directed multiple episodes of "2 Broke Girls," "It's Always Sunny In Philadelphia," "Happy Endings" and "Modern Family."
Age she started: Age 6 (1994)
Then: Whitman debuted as Meg Ryan's daughter in the film "When a Man Loves a Woman," then played the president's daughter in "Independence Day," George Clooney's daughter in "One Fine Day," and Sandra Bullock's daughter in "Hope Floats."
Now: In addition to reuniting with her "Arrested Development" co-stars for the new Netflix rivival, Whitman plays Amber on NBC's family drama "Parenthood."
Age he started: Age 16 (1994)
Then: Thompson made his film debut in "D2: The Mighty Ducks" and his TV debut on "All That," before playing one of the titular roles on Nickelodeon's successful comedy "Kenan and Kel" from 1996-2000.
Now: Thompson has spent the last decade as part of the cast of "Saturday Night Live," in addition to other movies and TV guest appearances.
Age he started: Age 10 (1953)
Then: Walken appeared as an extra in a number of TV series as a child before scoring the role of narrator in "The Wonderful John Acton." From 1954-1956, Walken and his brother alternated the role of Michael Bauer on "Guiding Light."
Now: A beloved star of stage and screen, Walken's most recent credits include a guest spot on "30 Rock" and a lead role in the movie "Seven Psychopaths."
Age she started: Age 13 (1993)
Then: Williams began her career in the early 1990s, guest starring on TV shows like "Step by Step" and "Baywatch," and in 1994, she made her film debut in "Lassie." When she was 17, Williams won the role of Jen Lindley on "Dawson's Creek" and became the youngest of the show's four lead stars.
Now: Following the end of the long-running "Dawson's," Williams has gone on to have an impressive film career, earning accolades since starring in 2005's "Brokeback Mountain." Her roles in "My Week With Marilyn" and "Blue Valentine" took her Oscar nomination tally up to three, and next year she'll play Glinda in Sam Raimi's "Oz: The Great and Powerful."
Age she started: Age 6 (1985)
Then: Ali began her acting career as a regular on "Sesame Street" and then, in 1990, she was cast in "The Fresh Prince of Bel-Air," starring Will Smith. She played Will's little cousin Ashley until the series came to an end in 1996.
Now: She has since pursued a singing career, but now recurs as Roxanne on the CBS soap "The Young and the Restless."
Age he started: Age 16 (1976)
Then: Soon ater playing the title character in "Bugsy Malone," which co-starred Jodie Foster, Baio was cast on "Happy Days" as The Fonz's cousin, Chachi Arcola. Of course, that turned into the short-lived 1982 spinoff "Joanie Loves Chachi," and then came "Charles in Charge."
Now: Baio became a reality star for a bit with "Scott Baio Is 45 ... and Single" and its successor "Scott Baio Is 46 ... and Pregnant." Now, he plays a version of himself -- a former actor who becomes a stay-at-home dad -- on Nick At Nite's "See Dad Run." How did he maintain a sense of normalcy after becoming so famous so young? "Simple answer: "my mom and dad," Baio said on "Anderson Live" this week. "They kept my head square and I never had any interest in any drugs ever. I've never done a drug in my life."
Age she started: Age 11 (1984)
Then: Bledsoe is most famous for playing Vanessa Huxtable on "The Cosby Show." She appeared on the show from 1984 until its final season in 1992. Blesdoe popped up on "The Cosby Show" spinoff "A Different World" and then went on to host her own mid-'90s talk show.
Now: Bledsoe returned to acting this TV season on NBC's "Guys with Kids." The actress told HuffPost TV that she wants her younger TV sister Rudy to guest star. "I haven't worked with Keshia [Knight Pulliam] in a long time -- I'd like to work with her again. I think that'd be funny," she said. "And she's such a lovely young lady now, I want her to come on and be really mean or evil or manipulative. [Laughs.] And really hot and sexy at the same time. Maybe she can try to steal my husband."
Age she started: Age 12 (1992)
Then: Dushku's career kicked off when she won the lead role of Alice in the 1992 film "That Night." She then played opposite Robert De Niro and Leonardo DiCaprio in "This Boy's Life" and after that, Arnold Schwarzenegger and Jamie Lee Curtis's teenage daughter in "True Lies."
Now: After high school, Dushku joined "Buffy the Vampire Slayer" and its spinoff "Angel" before winning a leading role in the teen hit "Bring It On." She went on to star in "Tru Calling" and Joss Whedon's short-lived "Dollhouse."
Age he started: Age 8 (1984)
Then: Green had the opportunity to co-star in "The Hotel New Hampshire" with Jodie Foster and Rob Lowe; the 1987 film "Can't Buy Me Love," playing Patrick Dempsey's little brother, Chuckie Miller; and in Woody Allen's "Radio Days" ... all before his 13th birthday. He went on to have success with "Can't Hardly Wait," the "Austin Powers" franchise and, of course, "Buffy the Vampire Slayer."
Now: In addition to lending his voice to Chris Griffin on "Family Guy," Green is also the co-creator, executive producer, writer, director and frequent voice of the Emmy-winning stop-motion comedy "Robot Chicken."
Age he started: Age 9 (1981)
Then: After minor roles, Wheaton first gained widespread attention in 1986 as Gordie in "Stand by Me." For the next four years, he played Wesley Crusher in the first four seasons of "Star Trek: The Next Generation," a role that recurred throughout the series.
Now: He's continued to have cameos all over the TV spectrum. In recent years, Wheaton has had two recurring small screen roles: an antagonistic version of himself on "The Big Bang Theory" and an uber-hacker on "Leverage"
Age she started acting:Age 8 (1990)
Then: Moss made her debut on the NBC miniseries "Lucky/Chances" and then had an arc on "Picket Fences" in the early '90s, but it was "The West Wing" that made her famous. From 1999-2006, Moss played Zoey Bartlet, the president's youngest daughter.
Now: For the past five seasons, Moss has starred as fan-favorite Peggy Olson on "Mad Men" and has been nominated for two Emmys for her portrayal.
Age he started acting: Age 9 (1979)
Then: After winning a Golden Globe for his debut role in "The Champ," Schroder went on to become a child star on "Silver Spoons," where he played the lead character Ricky Stratt.
Now: Schroder has worked steadily since his early years, making it through without much controversy (besides being a member of the National Rifle Association). He's had many notable TV roles including playing Mike Doyle on "24," a guest stint on "Scrubs," and of course, the three years he spent on "NYPD Blue" as Det. Danny Sorenson.