D.B.
Is there a children's museum in your area? We have several. A lot of museums increase income by hosting small parties. Our local environmental center has a small museum, a playground and an outdoor zoo for injured and rehabbing animals. They also provide small programs with a speaker and a few small animals. There's an enclosed area where a small child could crawl around. Maybe a few phone calls would get you some answers, or even referrals if the first few places don't do it.
Good luck. Otherwise I'd do something at home, scale back the food/decor (after all, he's only 1), and hire a couple of teens to help put stuff out, collect used paper goods, and take out the trash.