I'm going to add my two cents by agreeing with everyone else. I waiver is definitely the way to go.

I would also consider bringing as few animals as possible. And I would leave the rat home. I would bring maybe your boa, a ball, the tortoise, and the spider. They are the ones that (in my opinion) would be the most interesting to kids and still easily manageable. I guess if you brought the lizards though, they could see them through the cage, so maybe they'd be OK too.

And I don't know if I'd totally let the kids handle them. Maybe have them sit down and set your boa or the ball on their lap while you control the head (this would be easier with the boa). Then they can run their hands down his back and feel his weight without you totally turning over the business end of the snake to them (unless of course he produces one of his gigantic boa poops, then you're in for it!).

And I'd state somewhere in the waiver that they are non-venomous, non-lethal snakes, just to reiterate it to the parents.

I, like you, get super excited about sharing my hobby with the younger generation who are total sponges for good info. And I'd be the one to want to bring my entire collection just so I can point out to a 6 year old the subtleties between two normals. But remember that most kids see "a snake" and probably won't be able to tell you the difference between the boa and the ball at the end of it because they'll just be so excited to interact with these creatures.