I just checked on the chicks, and the one that had the poopy butt that I cleaned is right back to the way it was again?? What gives. Why dies it keep doing that?
She should outgrow it. You'll need to keep a close eye on her to make sure it doesn't get blocked up too badly. This can kill her if you're not attentive.
I agree with the vaseline method. It should help her stay clean, or at least be easier to clean off.