My grandson has never been hurt by recoil. I am taking him up very slowly. As you know a 223 is low recoiling. As a result of this, he has no "flinch" nor a tendency to jerk the trigger. His trigger control is awesome!!
For a child's first shooting experiences, I wonder about "adults" who knowingly put a high recoiling gun in the hands of a child realizing it is going to hurt. Shooting is to be enjoyed.
I can only go on MY experience as a kid. I had a daughter that loved fishing, but didn't really like getting up on a cold morning, LOL. She shoots a .22 fine, though, and I got her into the 12 gauge on clays (a gas auto, mild) when she was in high school.
As a kid, I started at age 6 with a Daisy and I didn't shoot my eye out. I got tutored by my grandpa and uncle. Uncle was an active NRA certified instructor teaching the boy scouts, so I had good instruction.
I got a Benjamin air rifle, .22 caliber, at age 7 and started stalking the woods around the house. First squirrel and rabbit were with the air rifle. I got a .410 at age 7, also, and it kicked the HELL outta me. I squatted down to shoot, was WAY too long for me, kicked me off my feet on to my butt. Worst part about it was the ol' man laughin'. I was afraid of that thing at age 9 and my grandpa started me dove hunting with 2 1/2". At age 10, I found it didn't kick with 3", who knew? ROFL. I shot my first doves at age 10 shooting that .410. I got a .22 at age 9, still have it, old Remington bolt M512, still very accurate. I was the terror of the squirrel woods, was head shooting squirrel at 50 yards with that thing by age 11.
My grandpa gave me HIS gun to hunt that year, 1963, outside Leaky, Texas. His gun was a .257 Roberts hand loaded with a 117 Sierra. Grandpa sat me down, told me not to shoot does that come along 'cause there'll probably be a buck along after her. Said he'd tell me why in a few years. So, I sat there as he walked up the hill with my uncle's .30-06 Winchester M70 determined to let the does go. About 45 minutes later, here comes a doe just a runnin' down in a ravine, and to my surprise, behind her was a nice 8 point haulin' the mail behind her down in a ravine about 75 yards off. I couldn't get a clear shot on that buck, then saw another coming behind and a little farther up in the ravine. I swung on it resting that rifle on a log that had been felled for the purpose. Got a good bead on the middle of the half of his shoulder I could see out of the ravine and fired. That gun kicked me back such that I couldn't see what happened and when I looked back, all I saw was a buck running off, thought I'd missed, it being a TOUGH shot, dead run and half hidden by the ravine. I was sick because I was a good shot, knew I was on that deer when the sear broke, but chalked it up to a hard shot.
Grandpa comes walking back down the hill 30 minutes or so later and says, "Heard ya shoot, you get anything, boy?" "Naw sir, I missed." I told him about the shot. He says, "Did ya go check?" Naw, I saw him runnin' off." "Always go check after the shot, you never know.", and he walks down to the ravine and looks down and says, "Well, if ya missed him, who shot THIS one?" ROFL I about peed my drawers, ran down there fast enough to qualify for the 50 yard dash in th e'64 Olympics.
We got back to camp, my grandpa bragged on me the rest of the week, made up for the laughing at my ineptitude with the .410 4 years previous. LOL! But, I had matured as a rifleman to that point to be able to use that .257, which is no hammer of Thor on the receiving end, but kicks a might harder than a .223, especially the way my grandpa loaded it. LOL 45.5 grains IMR 4350 behind that 117 grainer. A might hot. I've found better powder and bullet for that gun now days, but it will still hold 1/2 MOA. It's my prized rifle, not for it's caliber, but for other reasons. I've refinished the old stock, had a smith take the sight off the front and reblue it. It's still a shooter, though I've not taken it in a while. When I do go hunting with that rifle, I have the distinct feeling that my grandpa is looking over my shoulder from heaven and tellin' me, "Let the doe run, boy." "I'll tell ya why when ya get up here." I just HOPE I have a grandson to give it to before I check out. I have a 7 year old grand daughter at the moment and she's not real interested in hunting, either, though my SIL is a hunter. He should be home from Afghanistan in a couple of months.
NObody back then let kids use a .22 center fire for deer, was unheard of. That's what the .243 was for and the .257 before that. But, .22 bullets have gotten a lot better since the early 60s. The .22-250 is a popular Texas deer rifle with kids and the recoil shy. They can do much more than they once could do. Now, I ain't in to ARs, just not the kind of rifle I'm wanting. I prefer my bolt guns and my black powder, though I have a couple of SKSs, even took a deer with one. But, they probably do, even though they're light, reduce what recoil the .223 has. With a pull adjustable stock, they can be fitted for the little toots, too.
You're grandson done good with yours. Perhaps I'll have a reason to buy one in a few years, eh?