Thanks for all your replies, Kaika, Bebop, Pegasus, Tim!
I do know that girls of the middle school age are very insecure about their own appearance and sexuality. Confronting them, especially in front of others, as the "boob hawk" does, seems inappropriate to me. Despite their attire, these are usually good girls in class. I have never had problems with them, and some of them are quite creative in Art. So, yes, it's hard for me to think of approaching them about their boobs!
Patty