It's a slippery slope to say a .243 is big enough, next a .223 is big enough. How can I justify a .338 Federal when a .223 is big enough? Who needs a .416 Ruger if a .243 is big enough?
Shot placement is everything IMO, but sometimes things take a step just as you fire and a branch gets in the way etc.
Bring your flashlight and a canteen and everything will work out, (hopefully).
I would say have the kid practice and use the 6.5 just because it has a good reputation for penetration. When he grows up then he can use the quick twist .223 AI with heavy bullets like Big Stick. You have to walk before you can run.
whelennut
Please pass the popcorn. wink

I like to do my hunting BEFORE I pull the trigger!
There is only one kind of dead, but there are many different kinds of wounded.