I as in the same boat as you the last couple years with both of my kids turning 12 and wanting to hunt big game.
I also was wanting a rifle and cartridge that would get them started on deer but would suffice on bears/moose/elk later on without having to upgrade/change rifles.
I chose to go with the 270 Win as my wife already shoots one(Savage 111) and I'm set up for reloading for it.
My daughter is a bit taller with longer arms and my wife's 270 fit her well so she has been using it which she shoots well.
With my son, I had to purchase another rifle for him and went with a 270 Win as well. He is a bit smaller frame with shorter arms so I got him a Savage 110 Apex hunter with the built in spacers for adjusting the length of pull. He also shoots it well.
For both of them, they are shooting reduced recoil loads which puts recoil into the 243 Win territory. Down the road they can step up to full loads if they want to for larger animals and extending their effective range a bit.
Worked for us....
