Children need fresh air, sunshine and plenty of running and exploring. Keep their minds active and their health robust with games to play outside, various activities outdoors in winter, and learning with nature scavenger hunts, bird feeding, and such math and science fun as measuring big trees.
Try these old-fashioned games which children have somehow missed out on like tag, hide and seek, freeze tag, and swinging statue. No equipment is needed. Get those legs running and hearts pumping. Get outside for fun.