Little Big League (1994)

Billy Heywood is your average 12 year old boy with an amazing knowledge of the game of baseball. This could be due, in part, to the fact that his grandfather is the owner of the Minnesota Twins, and is his best friend. When Billy's grandfather dies, he leaves Billy the team. Now everyone is in an uproar that a 12 year old boy is running a major league team. He helps them become a team, and they help him become more mature.