Button size and usability

Hi there everyone,

Wanted to poll folks and ask, for an audience in the 10 - 18 year old range, what would you say is the smallest size I can get away with making buttons? Also, can anyone point me to some good usability resources on the subject? I googled for a bit and didn't turn up much, but I may just be doing a terrible job of searching.

Thanks in advance,

Dan P.