The motors aren't waterproof and don't need to be, they will run underwater, although it's not good to do for long periods of time. Puddles are not a problem. Lipos and water are a very bad idea. Nimh packs due to thier construction/cell type actually will also run under water (even open side by side packs with no shrink wrap). I've seen it.I wouldn't due it with my stuff and don't know how long they will last doing it but it does work.

Basicaly let the your 7 year old hit the puddles and have fun with no worries.