Hi L.,
I don't know how much you want to spend or if your son likes the water but the Niles YMCA lets you rent out the pool and multi-purpose room on Sat. from 2-4 (for 25 people) it is $65 + $50 refundable deposit.
What about Chick-fil-a?
I don't know how much Kidzoodle's birthday parties are? They are in the front of SoccerZone and I think they should be back up and running at the end of the month (from being down over the summer-something about heat makes them need to deflate over the summer).
A friend is having having her son's birthday at Barnaby's (pizza) and then going over to Strikes n Spares (but not doing the party package) but just paying for 2-3 lanes.
Is your son into planes? I thought I saw something that made me thing the airport might let you do something (upstairs). Then you could watch the planes land and take off.
I would think the South Bend Choc. Cafe would do birthday parties.
What about renting out a pavilion from the South Bend Park & Rec department (www.sbpark.org) and then you could do your own birthday party and then maybe take a hike or go to the park that might be connected to it.
I don't know how much Monkey Business in Toscana Park in Granger might be, we went to a party there and that was fun.
We rented out Galaxy Roller rink in Niles for a birthday party and that was fun, you get the whole rink to yourself.
That is all I can think of at the moment, but I'll keep thinking. :-)
C.