Illegal Bat

Question
I umpired a little league (13-14 yr olds) and I need your input. The batter hit a three run home run, the opposing manager then disputes the home run by stating the bat was illegal. Upon inspection, the bat barrel was composite material which is not allowed by the league (or Little League for that matter). What should the correct ruling have been? BTW, I did ask each manager before the game if their players were properly and legally equipped and was answered yes.
Thanks

Answer
Neil,

I am not trained in Little League rules, but I can answer in relation to NFHS (high school) rules. In a case of an illegal bat being used, the defensive manager has two options: (1) Take the result of the play, or (2) the batter is out and all runners return to their base occupied at the time of the pitch.

It's possible there are also ejections for it in Little League Baseball. I'd consult their rules manual, which should give the penalties for using an illegal bat.