S.C.
little monkey business in Western Springs is really cute - 3 year olds have a blast there.
I'm not at all associated with them - but really a cute spot - smaller - check it out anyway if you are close.
If you have older kids and not mostly 3 year olds then check out the Brown Cow in Forest Park - ice cream sundae parties. The family that owns it is fantastic and we have been to a couple of parties there. If allergies are a concern - they are very careful and understanding and use allergy free scoops etc etc etc.
http://www.browncowicecream.com/
Good luck