Okay, I know this one (and I am guessing some other moms of girls do too ). It really just depends on how much polish is is, and what kind (good quality polishes are easier to remove then the cheap, glittery stuff little girls tend to use). But, assuming it is regular, "adult" nail polish and not a huge quantity, nail polish remover should get it out. I have used non-acetone polish remover and that did not affect the hair. If a few flecks stick that a hard to get off with the remover, you can scrape them off with a fingernail.
Of course, if you don't want the polish to be easy to get out, then make sure it is a lot, and use glittery polish that will stick really well, and let it dry in there for a good long while . . .
It doesn't matter what you think, just that you do.