I agree that summer camp or some group activity where they're all in the same proximity would probably be the best starting out...maybe we could start more wholesome like Stryder said? And then ramp up to the big mystery? I'm still particular to a ghost hunt or a treasure hunt myself...though I also love the idea of an old-school like camp legend that they try to uncover, would be fun. 

Either way, I'm working on character ideas for my very tomboy presenting kid, she's very rough and tumble but I'm still sanding some edges down to get her ready and polished for the rp. :)