Rusty, Buster and Patch Versus the Opera — Adam Wallace

Rusty, Buster and Patch versus the Opera is the first book in a series about three brothers who love to have fun ... unfortunately this is at odds with their mother, who wants them to be classy. So she takes them to the Opera, but the Opera is boring for these three, so they go looking for fun. This means they end up back stage, on stage, under stage, under clothes, and selling hot dogs in the aisles.