I've got camp all week... HELP?!

So this week I'm babysitting my brother and one of his friends for four hours every afternoon. And I can't just let them play on their own, because I marketed it as a camp... I jus didn't get as many kids as I was hoping... I've got some fun ideas, but I don't know how well they will work until I try them. (Not to mention how long they will last!) At least they are sweet kids and I am getting paid!!