Little League International has adopted a new bat standard for the 2018 season. You can read about it here.
The quick summary is that almost all bats that were legal in past years are no longer approved for games, practices or any other activity related to Little League. Please take this into consideration if you are buying a bat for the upcoming season.
At LMB, we have adopted a house rule that disallows composite bats, except in the Majors A (and AA) division. Bats in all other divisions must be 100% alloy. All alloy or composite bats must have the USABat mark to be used.