D.C.
Absolutely! My daughter's 4th birthday party was at the zoo last year, and she wants to have her party there again this year. We had about 10-12 kids and their parents there. The animal presentation happens during the party time in one of the education rooms, and is about 15-20 minutes long, about three or four different animals. There is no petting or touching allowed, though -- my daughter REALLY wanted to pet the penguin that waddled into the room! Our guests' ages ranged from one year to 15 years, and they were all captivated by the animals and the presenter. I even learned something new about some of the animals. We had a penguin, an owl, an opposum, and a snake at our party.
I would suggest keeping the party itself very simple, because you need to carry everything in from the parking lot to the education center, and everything needs to be removed from the room after your party (so you will need to cart everything to the car before going into the zoo. There are no "party helpers" from the zoo, either -- you're on your own serving food, playing games, etc.
The rooms are decorated much like a classroom, but there is space to hang a banner or something if you want. There were some items in the room for games, something like duck-duck-goose with a stuffed animal, and some cards with animal pictures on them. I had the kids choose a card and they had an "animal parade" around the room, waving their cards and making noises like their animal. The room had a long countertop with a sink, some kid-sized tables with chairs, and several larger chairs for adults. We brought pizza and juice boxes and cake. The zoo has rules about straws, balloons, noise makers and such, so if these are included in your party, the guests need to know that they cannot take them into the park. I think they just asked that we take out anything we brought in (decorations, food, etc.), and put all the garbage from the party into the garbage can in the room, and that was the extent of our clean-up.
Our party was in the early afternoon, so on the invitations, I asked the parents to let me know exactly how many people would be coming so I could get their zoo tickets to them, in case they wanted to enjoy the zoo before our party time (remember kids two and under are free). And be sure to mention the parking fee on the invitations as well.
We had a blast, and all our guests told us they had a great time, too. After the party, everyone split up and went their own way in the zoo, but we ran into almost everyone from the party at least once that afternoon. The zoo staff was so helpful and nice about everything. If you are a zoo member, there is a (smallish) discount on the party fee, too!