The child suffered a cracked vertebrae after falling three storeys, but is expected to make a full recovery, said Sgt. Drew Grainger.
The boy's mother had left him alone with his young sibling while she went to borrow a vacuum cleaner from a neighbour. But when she came back, she was locked out.
"As she frantically tried to get back into her apartment, her five-year-old boy had managed to get out on the balcony, and climb up on the rail and fall to the ground below," Grainger said.
"Thank goodness the child was not seriously injured," he said.
Earlier this week, a three-year-old girl was also airlifted to hospital after falling two storeys from her home in Langley.
Grainger says these types of incidents are always preventable.
He says it should serve as a reminder to parents to keep patio doors and windows closed when leaving a child unattended.