Guide: How long to let kids stay outside in sub-freezing temperatures

With frigid temperatures across the country, health experts are warning about the amount of times kids should spend outdoors.

"Children are more temperature vulnerable than adults," said Dr. Don Duke, an emergency medicine specialist with The Christ Hospital Urgent Care. "They should not be outdoors for more than 45 minutes. Frostbite and frostnip can occur sooner and have greater severity in a child."

Duke, who has worked with the National Science Foundation in Antarctica, said maintaining normal body temperature requires balance between heat production (activity/play) and resistance to heat loss due to insulated garments.

Hypothermia may only manifest with fatigue and disinterest in activity in adults and children without recognition of low body temperature.

-- Here are some tips to avoid hypothermia:

- Dress kids in layers: If one layer gets wet, the child can remove it to keep moisture away from the skin.

- Choose warm fabrics: Use fleece and wool garments instead of cotton clothes, which will not provide insulation if they get wet.

- Cover extremities: Warm boots and mittens are essential because extremities are most prone to frostbite. Make sure kids cover their ears and nose and wear a hat to prevent significant heat loss from the head. The more you cover - the less heat loss.

- Limit time outside: Children should come inside often to limit their exposure to the cold, and they should change out of wet clothing immediately. Limit outdoor activity to 30-45 minutes.