I'm not meaning to be rude, but I can't understand the fuss here. Fuss is probably not the right work.
Why would it not pass a risk assessment if the kids have head torches and the road crossings are manned? Our local scouts do things like that all the time, as do many of the groups that stay at the centre next door to us. We have an outdoor pursuit centre right next to our house and stables, and they run about screaming half the night. Our horses and the farm animals around the valley have never bothered at all. As we speak there are ten orange tents in the next field! The only ones that have ever bothered them, and even then it wasn't much, was the brass band camp!
I think that when you have footpaths running through your fields you have to be aware of what you turn out. I ended up fencing half my footpaths off from the main fields just to make sure that the horses can't get near all the kids trekking about. I was more worried about the two nosy youngsters fighting for the kid's attention..
I am really sorry for the trauma that your horses were put through. I bet they won't use your path next time, and would contact you if they did! I would think they had as big a scare as your horses!