Calgary police and social services are investigating after one-year-old twins were left in a locked SUV in -20 C temperatures for at least half an hour.

A passerby spotted the baby boy and girl inside the vehicle, which was parked and not running in the lot of a downtown restaurant, on Wednesday morning and called police.

'Those little inconveniences can turn into major catastrophes.'—Insp. Luch Berti, Calgary Police Service

When an adult did not return "in a reasonable time," police started getting ready to break into the car.

Officers said they didn't want to smash the window and frighten the babies. But just as they started to jimmy the lock, the twins' mother returned to find it surrounded by emergency vehicles.

The children were taken to hospital as a precaution but were said to be fine, other than being a bit cold.

The woman told police she left the children in the SUV while she took another child, 5, to a doctor's appointment. Insp. Luch Berti said investigators suspect she was gone about 30 to 45 minutes.

"I think the mother genuinely believed she was going to come back very quickly and just like life is, those little inconveniences can turn into major catastrophes," said Berti. 

"In this case it was averted, but you know for the convenience of taking the child in for a quick appointment, it turned out it could have been to the detriment of her other two younger children."

Berti said criminal charges are not likely to be laid, adding that members of the Calgary police's child-at-risk response team and Alberta Children's Services are dealing with the parent.

"This one we escaped without tragic result, but definitely a lesson learned by the family and everyone of us that can vicariously learn by this," said Berti.