How young do you start your kids in Sports?

With my oldest turning 5 and him being very active…he has been begging me to play sports. At his age there are teams for Soccer and Baseball…so he is signed up and waiting for each season to begin. I know this will be a good way for him to burn of his energy and learn sportsmanship. What age did you start your kids in sports…. how has being in sports changed your child?