In looking over your photographs I was concerned that there was no protection from other shooters and their children. That was a problem for me. It would only take a slight lapse in concentration by a child or even adult to inadvertently end the life of another person. Too much to lose and too little to gain. You have my permission to call me a wuss but I prefer an inside range that offers some protection from other shooters or a very private outside area.
I am sure your child had a good time and you watched over him carefully. No doubt it was a fun day. And that raises a second issue. Is shooting to be another fun thing for a child to do before they can totally appreciate the consequences of a shooting mistake? Guns are serious business. Mistakes are made even by trained adults. The problem with guns is that you can't call that bullet back.
In reading through this interested discussion, gun safety has been promoted by the enthusiasts.....but I also think that knowing when a child has the maturity to safely handle a gun should be the determining factor.
The following is a pretty balanced approach to the pro and con of children and gun safety.
http://abcnews.go.com/US/parents-argue-teaching-young-kids-shoot-prevents-gun/story?id=22317419