WCB follows the USSSA Bat Rules
See Rule 7.01.C and Rule 7.01.D on page 5
In Short: You are able to use any big barrel (2 5/8 or larger) or Little League size barrel (2 1/4 inch) bat
These bat must have the "Thumbprint" you see below. Older bats may not have this thumbprint. Any retail store today will have youth bats with this thumbprint
Some retailers also sell bats with the USA stamp on them which according to industry standards do not perform as well as the USSSA bats so WCB also allows these bats to be used
7.01.C - All bats for ALL age divisions must be permanently stamped with the new USSSA 1.15 BPF Mark (Chart 7.01.C), or BBCOR.50 Certified Mark or made of wood and manufactured by a licensed USSSA manufacturer
7.01.D - Any bat permanently stamped with the official USA Baseball logo is legal to use