I have a rifle with a nice Williams peep receiver sight and Lyman globe front sight with target inserts. I wanted to keep that setup, but wanted to QD mount a 2-7 illuminated scout scope, primarily for low light hunting. It works well, but with one very important caveat: By nature of their inherent design, intermediate or long eye relief scopes (and pistol scopes) will have a very narrow and restricted field of view compared to normal 3 to 4 inch eye relief scopes. Because my rifle uses the scout scope only as a secondary optic for a limited role, I can liv with it.
Because you have such a scope already, you know this. Make sure your son is going to be happy with the setup, espicially if the scope is intended to be his primary sight. It will need QD return to zero capability, unless the peep is for emergency backup only.