there are 45 rules for baseball in MLB
There are 11 to 13 kids on a little league roster.
about every single one of them, lol
Just like any sport there is A LOT of rules and revisions that have been made to the game.
The basic gameplay rules are the same, but I'm sure there are certain managerial and coach rules that are different. I know that many little league coaches are not allowed to walk to the pitcher's mound. They have to stop at the foul line. I would assume there are slight changes in rules to NCAA as well, but nothing that would change the basic gameplay.