how much to charge?

I think MN Tigerstripes has a REALLY good point. Especially the last part about "typical greenie" behavior and the owners coming after you because you were supposed to make those horses "child safe." ANY green horse is going to have their moments, regardless of how calm they appear to me. Heck, my coming-3yo gelding is usually so perfect under saddle that people forget he's as young as he is, but even I wouldn't trust him with kids, even if the kids knew what they were doing, because he has the potential to have a "greenie moment." Unfortunately, it doesn't sound like these people's kids know what they're doing. I could be wrong, but usually people who are in the horse world deep enough (and if you have kids taking lessons, you're in more than deep enough) know not to buy a green horse for a kid. Also, people who are in the horse world deep enough wouldn't hire an untested, inexperienced trainer to produce "kid safe" horses.

I've had an immense learning experience with my gelding. He's the first horse I've worked with that was almost completely unhandled when I got him. He was 2-years-old, still a stud, and hadn't been handled more than just to be haltered and walked out to turnout a couple of times a week since he was 4-months-old. He was marginally halter broke, but had no ground manners to speak of. It didn't help that he was already 15hh as a two-year-old and is a draft cross. Every horse I'd dealt with before my gelding was already trained. I did retrain my old gelding from the ground up, but that's a whole different ball game than starting with a blank slate (my old gelding knew what to do, he'd just "forgotten"). I'd gained enough experience retraining my old gelding to put a decent set of ground manners on my new gelding (he's one of the best behaved horses on the property now...even better on the ground than some of the dude string horses!), but when I was handed a two-year-old green broke gelding with less than half a dozen rides on him, I realized just how much I didn't know.