if you search for the product in google or something like that you'll get a ton of hits. its all over the place.
as for the zapper i don't know about a 5 year old. some compare it to e-stim you'd get at physical therapy. there are some models of zappers that have several different settings, so you could use a lower setting. on lower settings it just feels like a tickle.
toolsforhealing.com has several models with really great descriptions, you could decide on a model and then search around for the best price on that model.