Believe it or not, Philadelphia has an overwhelming abundance of venues that host children's extravaganzas.
Two of Philly's favorite museums have birthday packages that allow families and their guests access to areas and exhibits that are normally not available or limited. The Franklin Institute and the Please Touch Museum are wonderful places to visit, but they're even more enjoyable during birthday parties. Each has an attentive staff that makes sure that your little ones party goes on without a hitch. Prices vary depending on number of guests and day of event.
Another choice is Kix & Giggles, whose prices range from $200 - $575. This place is a child's dream, with a huge indoor jungle gym, rock climbing and so much more. Guests will have so much to do and play with, no one will want to go home, and all the other moms will thank you for keeping their children happily occupied.
While these are just a few, like I said, Philly has so many options for children's parties. Too many to count, honestly. However, the ones listed above are venues that I have experience with and are worth checking out.