Hellobee Boards

my kid could do art all day long. maybe something like painting flower pots, include a couple bags of potting soil and some seeds? you could just put it all out on a tablecloth on the ground. we did my daughters 5th bday party at an art studio for kids that was fairy themed. They had these tiny wooden bird houses that they called "fairy houses" for the kids to paint, you could do that if you were worried about the flower pots being finished quickly.
then easy activities like bubbles is a great idea. i'd go for stuff that can be pretty self directed.

Oriental trading has some cheap blow-up horses that could be fun for the kids to run around with; they also have pin-the-tail on the horse, and a paper plate horse-craft kit.

http://www.orientaltrading.com/web/search/searchMain?keyword=horse

We attended a party like this for a friend's daughter. She was much younger - I think they won the party at an auction and had to use it that year.... They set up a bounce house outside, and it was a big hit while kids were waiting.

@PinkElephant: Since they're so cheap I'd probably do one per child and then have them keep them as a favor? Less drama so no kids are fighting over them. OR have enough for every kid minus 2 to 4 (the 2 that are riding the ponies/2 that are next up).

Lots of cute ideas. Just clear them with the place first - a lot of these in the same area as the horses would totally spook them and wouldn’t be allowed, fyi.

Planting flowers in little pots for each kid to take home is a cute idea!

I would go to Michaels and get a small canvas and have them paint a horse or something. Or horseshoe. My daughter is around that age and she would take time to decorate and draw it.

Or "Pin the tail on horse"

@PinkElephant: you have a lot of awesome ideas here but yeah, I think a craft where no one really directs or supervises is ideal (and so - make it cheap!). They don’t have to sit down together, no one cares if they finish or how they approach, doesn’t require lots of oversight. I’m guessing most of our valentines got tossed immediately but it was fun and cute while they did it! And some kids who loved that stuff could stay longer than others.

I would be hesitant to do a piñata if 2 of the kids will be riding during it. I know my kids would be so sad to miss the piñata!

My kids love crafts but could also entertain themselves if their friends were there and balls or ring toss stations were set out. I would avoid any organized activities.