The Little League bat rules are completely changed starting in 2018.
Generally, bats that were previously allowed prior to 2018, will not be allowed any longer.
The main Little League Bat Page is at the link below:
http://www.littleleague.org/learn/equipment/baseballbatinfo.htm
Minors & Majors
--Must have "USA Baseball" marking
--2 5/8” barrel maximum
Intermediate (50/70) & Junior
--Must have "USA Baseball" marking or BBCOR Standard Bat.
--2 5/8” barrel maximum
Bat Selection Guide