Re: Youth builds
Worriers or warriors? My limited experience shows that worries increase (not decrease) with age. Anyway, my sons will be rocking .22LRs until they can comfortably shoulder a 700 youth .243win. That is enough for any whitetail deer in our area. If they shoot it enough to need a rebarrel then great. I'll have a donor action for a custom build. If they don't then I'm not out a huge investment.
What are you planning to shoot with the rifle? If target practice, then I would go with the cheaper to shoot round. If you have an application in mind, then choose accordingly. If you need an excuse to buy/build another rifle (and who among us does not?) the choose the caliber you like best.
Then again for a young daughter, the .223 may recoil less than a 300 blackout.