C.R.
For my daughters 4th B-Day we did her party a Chuck E Cheese -She had a blast and there is plenty of room for 20 kids. Only thing is it is high priced. Another idea that is less expensive would be a B-Day party at McDonald's. We did her 3rd B-Day party there and it was very easy.
Another idea would be Bump City - Google emerald city gymnastics for details.
Hope you find something that works for you:)
C.