My exes g/f who spends quite a bit of time with my children ignores them in public if they happen....?

First of all, that is sooo wrong. But, if I were you, I would probably tell my children the truth-that sometimes people are mean out of stupidity. I would explain that she doesn't like you for whatever reason, and it makes her act mean sometimes. I would also tell them that it's ok to tell her how they feel when she does things like that (next time they see her). And also let them know that you love them no matter what. If you're able to have civil conversations with your ex, it might not hurt to let them know that your children are being hurt. Make it short and sweet and to the point with all involved. Good luck with whatever you decide.