Starting in 2018 new Bat Standards will be in place. Little League International has sent out an explanation below.
2018 New Bat Standard
Beginning with the 2018 Little League season, non-wood and laminated bats used in the Little League (league ages 12 and below) shall bear the USA Baseball logo signifying that the bat meets the USA Baseball Performance Standard. All BPF (bat performance factor) – 1.15 bats will be prohibited beginning with the 2018 season. Additionally, starting in 2018, the bat diameter shall not exceed 2-5/8” for these divisions of play.
A list of approved composite barrel bats can be found on the Little League website, at: www.LittleLeague.org/batlist.