Can I be so crude to ask, but why the bull barrel for a youngster? That's a lot to lug around. I would go for a larger, slower bullet with more meplat in a standard contour barrel. The larger bore would reduce some of the weight, and yield a larger wound channel. .44 Mag would be a suggestion, also .357 Max or .45LC. Recoil should be about the same I think.
Don't get me wrong, It is a beautiful rifle. It's just that I got rid of my small caliber bull barrelled rifles long ago. They're fine for bench or varmint shooting, but nasty to lug around in the woods. They won't sling properly unless upside down. I'm also not fond of .243/6mm for deer. I have other Handis that kill more efficiently. My 6mm Rem Model 7 poked right through deer, and they ran and died. Where?

Now it's time to go find him and drag him out. Not fun. Hit with a .445 super mag or a .45.70 in the same vitals, they crash right there and don't get up.
You're a neat grandpa, and I'm trying to do the same with my two grandsons. One's getting a 7mm-08 and the other a .357 Max. Both Handis.
Sorry to sound like a nay sayer, I really do think what you're doing is very cool.
Pete