Sounds great.
Find, and dam, a stream that runs into the river. Find cool rocks -- collect the little ones and climb the big ones (bearing in mind that kids find LOTS of rocks cool). Find flat rocks and skip them. Find cool plants. Pick berries (if available) and eat them. Observe and/or catch (and release) crawdads and/or snakes (non-venomous, obviously) and assorted bugs. Teach the kids to whittle (one of the camps my son goes to lets the littler kids do this using vegetable peelers and it astounds me how much pleasure he derives from this). Build forts. Play capture the flag, kick the can, and/or tag. Have a scavenger hunt. Explore different techniques for building a fire (flint, magnifying glass, matches ...).
I think the outdoor camps my elementary schooler goes to have about 4 kids per adult, though some of those adults are youngish teenagers, really (counselors in training) -- but old enough to supervise when themselves supervised. Things to consider will include how to manage when an adult wants a break (or you can stagger shifts, or days) and how you'll manage if someone (kid or adult) is sick or injured -- you want a bit of redundancy, ideally, but if there's also the option of a safe retreat spot (e.g. you can go to the house in a pinch), this is less of an issue. You may want to plan some activities for stormy days, or at least think through where you'll go (if anywhere different) and how you'll manage that sort of thing.
