Depends on how much ammo you expect to shoot per year.
I wouldn't bother with 17hmr as it is expensive.
I have a 243 and it works well. haven't had a bang flop yet but they don't run far.
I have a 308 too, with 110 grain bullets and a good butt pad your 11 year old should be able to shoot ok until he grows a bit.
I would get the 308. It just works.
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