You can't do the Nutcracker without boys, and this production has some good ones. I'm guessing these have been at it since they were quite young, because I'd guess the oldest might be 17 and the youngest might be 15, but they do some amazing moves. What looks like a changement with two (or is it three) beats. Cabriole with height, crispness, and extension. Triple pirouettes. And they make it look easy.
I guess you could make do without boys. You could dress up some girls in boys' costumes, but how many girls learn to do lifts and such? And how many girls want to go on stage dressed as a boy? I'm guessing it doesn't really fit the mental image of how they would want to be seen.