Stuck inside? Try one of these get-up-and-go games -- appropriate for toddlers on up -- from Active Start for Healthy Kids by Steven J. Virgilio, Ph.D., a physical education professor at Adelphi University, in Garden City, NY:
Fun for one
Play "Snake in the Grass." Hold a jump rope flush to the floor, then wiggle it back and forth while your child tries to jump on it and stop the "snake."
Fit for two
Give one child a foam ball, beanbag, or stuffed animal. Shout out "Elbows!" and have the kids trap the toy between each other's elbows while shuffling across the room, taking care not to drop it. Choose a new body part -- "Belly buttons!" "Foreheads!" -- and send them back.
For a playdate or a party (though this game's still fun for one), space the kids out around the room. Put on some upbeat music, tell them they're famous athletes, and ask them to mime different moves (shooting a basket, dribbling a soccer ball, etc.) when you call out the name of a sport.