Well to be honest when my cousin and I were young 5-8yrs old, our pop's drug us out to shoot their 03A3's every Labor Day in prep for the upcoming deer season. While we didn't actually hunt with those rifles, we did shoot them several times whether we liked it or not. What came from it was that we learned not to fear the recoil or noise from them. It has made us both very good shots through the years.
My oldest grandson bluntly told me, just after his 3rd birthday, he wanted to shoot himself a hog. This was taken by me as tongue in cheek, but he simply wouldn't let it lay. The biggest issue was finding something that would fit a little boy of his stature, as has been mentioned fit can be everything. I told him if he was serious he would have to hold the rifle himself, which I was hoping was partly a way around it for another year or two on my part. This was all well in good until he asked if he could look through the scope of my Ruger Compact one afternoon, not long after his last insistence. I said sure and set it up on the sand bags, where he promptly squared off with it, and then proceeded to raise it up and look around the pasture. He called my bluff and said, "hey this would work for me right". The rifle is chambered in .308 and after a few days on the net looking over load data, I settled on the reduced loads using H-4895, and the 125gr bullets. He started off with three rounds all of which teared up his eyes, but he wiped them off and went on with it. I finally got him settled in to hold the rifle properly which was accounting for most of his recoil issues, and he started shooting some nice groups at 50yds. This was my imposed range limit. I then started setting up life sized paper archery targets on plywood at various ranges out to 75yds and would call out which number from left to right I wanted him to shoot. He had to hit three rounds in the kill zone, on all of them, before I would let him hunt.
Three weeks before his 4th birthday he shot his first hog and dropped it in it's tracks,
I shot my first deer using a 30 Carbine at the age of 6, and then followed up with three or four a season, for many years following, using a Win 70 in .243. When my daughter was 6, she was shooting this same rifle plenty good enough for a deer out to 200yds, but it wasn't until she was 9 did she get a chance to make a shot, where she argued with me about using it or my 25-06. I finally gave in, as the deer was slipping further across the pasture, she then reached out just over 185yds with it, and dropped her first buck in it's tracks.
I have found that even if the fit is not exact, with me and my daughter, and grandson (s), if they have the desire, they will get the job done if they have the desire. The thing is having the desire to start with. In our family everyone hunted, it was a yearly tradition where we all got together and shared the experience. Nowadays, most folks don't have the time our parents had back then, to get out with the kids and share their experiences with. We make it fun, and my daughter and her three, have all wanted to join in on it. It is simply something we can all do together, and enjoy it when we do.
As for the young folks in pictures, with this, that, or the other, well I have personally seen many youths who were much better shots than their adult parents were. They just go about it as something to do, rather than something to prove.
Since his initial hog, the oldest grandson now has close to a dozen under his belt with a 6.5x55 and the same .308 with standard loads. He also got a nice doe for his first deer and two nice bucks to follow that one. The doe he shot using the 6.5x55, and the two bucks were using the 25-06 on one, and the .308 on another. The only rifle which actually fits him is the .308, and he would MUCH rather now use the 25-06 go figure.