Donna...I know how you feel and I am with everyone else on this. Knowing that your MIL does not really wash hands so well either, that would make me even more worried about leaving the kids. I am sure everything would be fine, but why add the extra worry and this way, you can at least know that you did everything to protect the kids so they would have a great party. Normally, I would say that kids are exposed at any place you go, but I do think that since the party is so important and your MIL doesn't wash hands like we all do, I would keep them home.
TRY to live each day like it were your last