Where in Wisconsin are you located. I'm in Twin Lake in the SE corner of the state.

As far the the pet bugs go I think hissers are the best for a first choice. They are Large, handleable, easy to care for, and harmless. Pretty much everything you want in a pet bug. Mantids are very very cool but any adults or close to adults you get will likely only live a few months to MAYBE a year at the most. Millipedes are cool but they hide a lot and if you want to see them you usually have to dig them up. As far as the giant centipedes go I'd certainly not recommend it for a young child as they can be very aggressive and their bites can hurt like the dickens and sometime maybe worse.

If you want to spend a little more money and get something a little more exotic I would also recommend vinegaroons and tailless whip scorpions. though handling is a tiny bit more of an issue with them, especially the TL whips because they are so fast. If you've watched Harry Potter and the Goblet of Fire you have seen a giant CGI version of the TL whip scorpion.

I do and insect show for schools and libraries and the kids love it as much as my reptile shows and to be honest I think I am more into the bugs than the reptiles myself.

I love your Avatar by the way. Quite possibly my favorite animal of all.