WATCH: Children's hospital issues dire warning about frostbite

St. Justine Hospital has issued a dire warning about the dangers of frostbite — saying young children are particularly vulnerable.

The children's hospital posted graphic photos on its Facebook page of young children with red, swollen and blistered feet.

“Intense cold can quickly cause frostbite. Young children are particularly at risk. Keep them warm and dry,” the post read.

Frostbite happens in cold temperatures when blood vessels close to the skin constrict to protect the core body temperature.

Young children are particularly vulnerable, because children tend to lose heat faster at their extremities, and don't often notice there's anything wrong.

In addition, very young children can't often communicate their discomfort to parents.

Doctors at the hospital say a six children were brought in with severe frostbite during the holidays, and the recent cold snap.