I would not take on the responsibility of training these horses if I were you, especially for "child safe" horses.
Like the others said, taking on 5 untrained horses is a lot of work and responsbility for someone who has never trained from the ground up before. If you aren't working with a knowledgeable trainer there is a huge margin for error and you're very liable to get yourself hurt or screw up the horses. I like Smrobs's idea about having them get an experienced trainer and working with that trainer to learn more.
The other red flag for me is that the owners want "child safe" horses out of this endeavor. Making a horse "child safe" isn't something that happens after 30 or even 60 days, especially when you're starting with essentially feral horses. In my opinion you're setting yourself for a bad deal. The first time one of the horses you've trained does something a typical greenie does they'll be screaming about how you were supposed to make them "child safe".
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.