I agree Charlie I'm afraid, I have done a few kids gigs at our local Hungry Horse and the kids were more reserved due to not knowing each other, but maybe something simple like a hula hoop comp or limbo may break the ice and get them out of their shell.

Or another game I play with large groups is Heads & Tails - play music for them to dance to then stop the music and ask them to choose heads or tails (put their hands on their heads for HEADS and hands on bottoms for TAILS) you get to get chunks of kids out at a time so doesn't last forever.

Good Luck