Oshawa Fire Services (OFS) said it responded to a carbon monoxide call Friday afternoon and escorted visitors and staff outside the gallery. The kids, who were attending an art camp, were taken to Lakeridge Health for "precautionary observation and treatment as required," OFS said in a statement.
Vincent Gratton and Stephanie Gratton's children are seven and five years old and attended the camp.
Vincent told CBC News that his wife told him that when she picked up their kids Wednesday "it smelled like gas" and she told the staff but that "no one did anything."
He added that when their son returned from camp Thursday, he slept for 13 hours which was unusual for him.
OFS and Enbridge Gas are at the scene and working with the venue to investigate the cause of the leak.