Herd, not heard.
And not sure if you are calling 9/11 year olds geriatric or not? But those are not even close to being old. And are they yours or the camp horses.
If you are comfortable telling us you don't have the experience for this, you really need to do the camp a favor and tell them that too. From what you are writing I don't think you are ready for this, nor have the background to keep this kids safe.
Please reconsider doing this if you are going to be the ones working directly with the kids.
If all you are going to be doing as barn boss, is saddling and feeding and such, that is one thing, but if you are going to be trying to teach kids, and keep them safe that is another.
Horses make me a better person.