Little League has various substitution rules. Two for regular season and one for post season. In the regular season, we can use rule 3.03 or 4.04. As a league we use rule 4.04 so this will address that set of rules.
3.03 is where we only bat the 9 in the defensive lineup. 4.04 is where you bat everyone at the game and have free defensive substitution.
Under 4.04 there have been some questions.
Q: What happens if a player in the lineup has to leave before the game is over (for any reason)?
A: You skip that batter WITHOUT PENALTY.
Q: What happens if a player arrives late?
A: That player is added to the end of the batting order. NOTE: It's the coaches option to add him. It's not required to add him at all.
Q: What happens if a player is injured, ill, etc. and they leave the game but return to play later in the same game?
A: They are inserted back into their original position in the lineup.