A Special Location
Why pay to rent out an expensive venue when your backyard is open, available and free?
The truth is, as long as you have a sizable enough space for kids and their parents to congregate, it's just as good a place as any to hold a b-day bash. If something gets damaged, no one's keeping your security deposit, and though you might have to tackle a juice stain or replace a vase, it'll be peanuts compared to the amount a venue might demand.
Your own property might not seem spectacular to you, but as long as you and all his little friends are there, it's the only place your child will want to be.