For 2011 Pony Baseball has made some changes to their rules regarding bat barrel diameter.
“Equipment, 8 (c) Wooden, metal, graphite or ceramic bats manufactured for baseball play, which are round and not more than two and five eighths inches in diameter (for Shetland, Pinto and Mustang effective in 2011 and Bronco, Pony, Colt and Palomino in 2012) at the thickest part, not more than 42 inches in length, are acceptable.”
So the older kids in Pony baseball can still use a 2 3/4″ barrel baseball bat for 2011 if they are in Bronco, Pony, Colt and Palomino.
The younger kids must now use a 2 5/8″ diameter barrel baseball bat for 2011 Pony baseball.
Also note, there is no mention of composite bats in the Pony Baseball rule changes for 2011