Can They... Go Outside?
By Deborah Skolnik, Parenting (http://www.parenting.com/article/Baby/Health/Winter-Health-Guide)
Windy days can feel much colder than the actual temperature. When deciding how long kids (and adults!) can play outdoors safely, the windchill factor is most important. Keep this chart handy:
Green Zone: 30°F and higher
Kids can usually play outside comfortably when it's 30°F and higher -- just layer their clothing and make sure they wear hats and mittens. Offer water often (it helps regulate body temperature), and watch for signs that they're getting chilled. If they're shivering, bring them inside even if they insist they're fine. Feel babies' hands and (if possible) feet regularly to see if they're turning icy; also watch for unexplained fussiness. It's a good idea to come inside for a quick break every 40 minutes or so, just to warm up a bit.
Yellow Zone: About 20°F - 30°F
Be cautious. It's okay for your kids to go out, but follow the guidelines above, and expect to see signs of chill sooner -- take short indoor breaks every 20 to 30 minutes. It's especially crucial to layer older kids' clothes, since they may ditch their coats if they get sweaty and so need to be wearing more than a thin shirt underneath.
Red Zone: Below 20°F
30° = chilly and generally uncomfortable
15° to 30° = cold
0° to 15° = very cold
-20° to 0° = bitter cold, with a significant risk of frostbite
-60° to -20° = extreme cold; frostbite is likely to occur
-60° = frigid; exposed skin will freeze in one minute