I have a similar situation and it is so hard! It's hard b/c partly you know it's kid stuff but you are on the side of your own kid and you hate to see them pushed around, I totally get it. Plus, you want that time to "yourself" to have the kids playing and you be able to hang out a little bit with the other mom, so you're caught in the middle. I agree that keeping the kids close to you is a good step. If you can see then and help descalate the situation first, that will help. And yes, you may have to go home early if the situation evolves into hitting and pushing. Something I've also done with my daughter is try and tell her before we go to this person's house is that no matter what the other child's behavior is, I expect her to do the right thing. She needs to say no and get help if necessary. I make sure that my standards are still high and enforce them no matter what, because sadly I guess, life lessons start at 3...not everyone will treat you nicely and you still need to the right thing. I do think part of it is the age...it's hard for this age to share, play together, etc. It can and should be done, by all means, but with some kids it takes time. Hang in there...I hope you work it out!