Not to take a thing from yer kids great shooting, but seeing the group, I recall a post many years ago by someone coming back from Compton or such...
There were adults with kids on a kids range and so this chap said a parent volunteered to stay so he went for a shoot.
Came back and his kid had a perfect group like that of your son's. When asked how he managed that (he was a young tyke as I recall) he shrugged and said, "It was easy, I kept pulling just the ones that weren't perfect and kept shooting till they all were!"
Now that is the making of a true traditionalist!
Congrats to your son. Nothing like youthful eye-hand coordination to help accuracy!