The bat rules for 2012 have been posted on the Little League web site.

Here are some excerpts/highlights:

• For the Little League Major Baseball Division and below, the moratorium on composite-barreled baseball bats remains in effect.
• For Junior League Baseball, composite-barreled baseball bats must meet BBCOR standards, and must be so labeled.
• For Senior League Baseball and Big League Baseball, all bats with non-wood barrels must meet BBCOR standards, and must be so labeled, and must have a drop of no more than minus-3.
• The moratorium on composite-barreled bats does not apply to softball.
• The batter is out for use of an illegal bat. In this context, a bat that is dented, cracked, missing or bad material on the grip, etc. is not illegal, although the bat must still be removed.

You can (and should) read the details at http://www.littleleague.org/media/newsarchive/2011/Sep-Dec/LLAnnouncesBatRuleChangesfor2012Season.htm, including links to the approved composite bat list and the full text of the affected rules.