Dunlop was worried, then shocked, to learn what the fuss was about.
The boy's crime? Shopping in the store by himself.
Dunlop was the one who was really in trouble — he says he was given a lecture for being a bad parent.
The toy company has a policy that children under 12 can't shop without an adult because of safety concerns. Dunlop said he wasn't aware of the rule and finds it ridiculous.
"I didn't send him, you know, to fight wild animals or to do something dangerous," Dunlop said Thursday.
"He was going to do the most ordinary of things — buy something in the mall."
The stay-at-home dad said that after they got home from shopping Sunday, he fired off a letter to the company and the Chinook Centre mall, demanding apologies.
Dunlop describes his son, Tadhg, as well-behaved and independent. The boy gets to school on his own and shops on his own. He has been to the Lego store dozens of times before, by himself, and spent money he saved up from shovelling and babysitting.
But on Sunday a worker at the store asked him how old he was, then called mall security.
Tadhg said he felt "surprised and ... sad."
His father recalled that the security guard told him that child abductions are a concern and "if you don't see how leaving your child alone in a store is dangerous, then you are a bad parent." A store manager added that any good parent should know a child can't be left in a store unattended.
Dunlop said he can handle people calling him names. The worst part was that his son was detained — not allowed to be in the store alone and not allowed to leave without his dad.
Lego spokesman Michael McNally said in an email that the company's primary concern is for children's safety.
"As this customer was under the age of 12 and unaccompanied, our store staff followed our guidelines and alerted mall security."
Paige O'Neill, general manager of the Chinook Centre, said there is no age restriction on who can be in the mall. "Should security personnel come across a child, youth or any guest who appears to be in need of assistance, we will engage and assist to ensure their safety and well being."
Dunlop said he has received responses from two Lego officials in North America, who stand by the company's policy. He's considering fighting further up the ladder.
"If this was to get to Lego head office in Denmark, there'd be four Danish guys saying, 'Well, my nine-year-old took the train to Hamburg last weekend on his own, so why would an 11-year-old not be able to shop at a Lego store in Canada?'"
For now, Dunlop said, he and his family are boycotting the store, but not the product. It's Tadhg's favourite toy.
"That would be cruel to my kid. He's passionate about Lego and, really, I believe in the product."
— By Chris Purdy in Edmonton