Stubblefield Lake would be my recommendation also. First of all it's small so you won't be inundated with people. I've never camped there but have been there several times to access the Lone Star Trail, which has a trailhead at the campground.
Since I've never stayed there, I haven't done a thorough look at their facilities, which appear scant.....restrooms with hot showers, and that's about it. I've seen mostly tent campers there with maybe a pop-up camper or two.....they are not set-up for anything larger. I don't even think every site has a water spigot.........they're centrally located.
Another recommendation is Double Lake close to Cleveland. However, it's larger than Stubblefield.
It's good that you're starting your son out while he's young. If he takes to it, he'll be hooked for life.
