C.C.
My daughter has been to parties at Pump It Up (both locations), which is always a big hit with the kids. Also Cobb's Ranch has parties where the kids can ride the miniature ponies. Playland in Roeding Park rents out spaces as well. A friend of my daughter's had a pirate party there, and they all played on the big pirate ship. There is a tea party place in the Tower District. It's on Olive Ave but I forget the name. I haven't been there myself but have heard it's lots of fun - they have dress-up clothes, fancy china, etc. Also we've been to a couple of parties at the Little Gym. It's fun for little ones.
I hope this helps!