I have a 6 y.o. grandson and am planning my first purchase for him, so I know what you are going through. Of your choices, I would definitely buy the .308. Ruger makes the American in an all weather compact model. The .308 has an 18 inch stainless barrel, carbon composite stalk and weighs in at 6 lbs. The 18 inch barrel and 6 lb weight makes this a very maneuverable gun. However, this combo will most likely come with a fair amount of recoil. Therefore, I'm planning on buying my grandson a .308 and will have a muzzle break installed, which would basically take the recoil to somewhere around a .223-.243. It would offer the most versatility. Also, a synthetic stock makes this gun great in all weather. I'm planning on having the stock dipped into a camo scheme for him, that would really make his gun unique. Pitch that possibility to her as well. Regardless of which .308 you would purchase, a muzzle break would be a great investment for a younger person. Good luck!