Birthday party ideas for a 2 year old?

We want to have a small B-day party for our son. I don't want anything to extravagant, but I want it to be fun for all the kids invited. Most of the kids will be between the ages of 2-4 and then my nephews are a bit older (8 and 9). We were thinking Chuck e Cheese, but their parties are a bit too much for the age group we'll have and I don't want to pay $11.00 per kid when most of the stuff is unnecessary. Most of the kids won't eat 2 slices of pizza or drink soda. We'd have to pay extra for parents to eat and drink. We'd also need it on a weekend, so it may be impossible to have a walk-in party with 20 people. Any ideas?