My 7 year old Grandson shot a buck and a doe with a .223 last season. Both went about 50 yards, shot broadside through both lungs. That said, I’m not a fan of the caliber. But it works if you get good broadside shots at reasonable distances. I think he’s using a 6.5 Creed this season.
A .243 works well for deer, real popular with kids, but I’d prefer to give them a 7mm-08.
Folks will say overkill, but I’m a fan of .300 WSM and .300 WM. I could kill lots of deer with a .308, but I’ve become a magnum fan. Long distance shots aren’t a problem, very little bullet drop, and you never run out of horsepower. Nor are frontal and quartering to you shots an issue. Seldom does a deer go more than a few yards, many buckle in their tracks. I’ve killed 16 bull moose with those two calibers, never had to track any of them…I saw them all drop.