Good decision. Even though you are only upping the load 10gr in each department, I would still have your son shoot it. The difference to you as a full grown man would be negligible, but maybe not to your 10-year-old boy. cayugad hit the nail on the head with regard to shooting in awkward positions in hunting situations. I shot a deer on Saturday from a treestand, and even though the position didn't seem awkward at the time, my nose still got hit pretty good by the scope and I discovered a bruise on my right bicep from the buttstock. The point being that even a not-so-awkward shot still may result in not being able to get behind the rifle properly, and a good scope bite - even from the load you worked up for your boy - could result in him being afraid of the rifle the next time he shoots.

In the end, you know your boy and we do not. You are the one best equipped to decide for him, and it sounds like you have a good combo there.