Had one of those...who's 21 now. Involved them in some sport. 1 at a time imho. A good age is 7 ish +. Rotate sports so they get a flavor of what they like and dont. Mix in organized (paid) and free sports activities (running, biking, skating surfing). Participate and practice with your kid. Make it as fun as possible. Be into it if they are (even if you have to fake it). Dont make your kid play a specific sport, but make them do something. Doing nothing wasn't an option for us. Good luck and have fun.