Being the resident gun enthusiast in the family, with a ranch to hunt, has provided me with experience training lots of nieces, nephews, sisters in law, cousins, and my own kids.
I have seen the most success with Rem 700 youth models with a shorter stock in 243 caliber. I handload with a warm and not maximum dose of IMR 4350 and Nosler partition bullets in 100 grain. I even bought a left handed youth model for those who are left eye master. I use a Nikon 2x7 matte scope.
I also have the New England single shot models, but I like the bolt gun's ability to take a faster second shot if the youngster and/or first time hunter gets buck fever and yanks the trigger.
We have taken at leas t 50+ deer over the years with the 700 youth models. In fact, I like to take it with me on the 4 wheeler because it is so compact and handy, plus it works on coyotes and hogs, which always seem to show up when you don't have a rifle with you.
I have also been meticulous with eye and ear protection, and it is a good choice to get the youth sized glasses and hearing muffs.
Good luck. It has always been more satisfactory for me to watch someone take a game animal that I have helped introduce to the world of hunting.