In regards to you keeping him and handling him in the future, have you considered finding a trainer/lesson barn in your area that'd be willing to work with you and Teddy? Limited knowledge is something easy to fix, but you have to be willing to search for the answers that you need. Even if you don't find a lesson barn that's suitable for youngsters like Teddy, you COULD contact a lesson barn and ask specifically for lessons that involve groundwork, learning how to lunge, what to do with pushy horses, how to move their front and hind quarters away from you, etc, and explain your situation to them. You'd want a barn/trainer with a lot of experience and the patience to train both human and animal. What I learned when I was adamantly lessoning is that I didn't want to deal with the trainers who didn't take the time to explain thought processes, both human and horse, to me, and if they wouldn't let me step in and try for myself, I high-tailed it out of there. I'd suggest looking for a friendly person who's as rooted in teaching both horse And human what to do. It's almost like apprenticing, the difference is you're still paying them as you would for a lesson. You'd benefit a lot from those kinds of lessons in the long run, both with Teddy and any horse you or your children acquire in the future.
In regards to selling him, have you considered leasing him out to those who event instead? Someone else would get to enjoy him for what he is eventer wise, you'd still get the pleasure of owning him and being able to do what you want with him, plus if it's not a free-lease and it's drafted out, you'd get some financial help from the person leasing him. You can even specify that you want to keep him on your property, something people do all of the time, and you already have a lease prospect in your son's friend. It could easily be the best of both worlds.
Regardless, he is adorable. I really hope you get to keep him. :)