Good topic. I'll chime in.
I cut my teeth waterfowl hunting. Been hunting since I was 10, 29 now. Started going long before I could even go with the gun just to watch. I'd just deer hunt one or two times a season during 6-day..maybe get a shotgun permit when I was younger. Wasn't really dad's thing, so naturally wasn't really mine growing up. Ducking though, there was always something to watch..notice..tinker with without having to sit absolutely still. Could talk and move around, didn't have to sit in silence. So it was more social in way. Not saying that isn't applicable to deer hunting, but it is different. Deer to me is much less social and more of a solo venture. I got more into as I got more independent and learned a lot on my own. But to that point, I had a lot of motivation just from the fact I waterfowl hunted so much.
There is stuff out there that flat out says starting kids earlier (and having them go through hunter ed younger) will result in kids that become more frequent hunters. 3 out of 5 10 year-olds will go on to be a hunter past 16. A kid that goes through at 14..15, you're then talking a kid or two that age that'll stick with it. It's a big deal in the grand scheme of things in terms of hunter numbers. There's definitely merit in starting them young. More exposure is a big deal. It isn't about them harvesting something instantly. They need time afield to connect all of the dots, they shouldn't just land at harvest. I argue all the time guys that try to put their 10-12 year old on a slammer buck and I think it's incredibly counter-intuitive. I can appreciate the fact they are making it about their kid, but if it's some underlying vicarious thing, I'm not sure the intention is right and if it's truly about their kid. We should always be striving to grow as hunters; how does one grow and develop skills by doing that at a young age? You just made it a novelty at that point and lose them IMO.
Start them young, make it truly about them. Just supervise, coach them to an extent, but let them make the calls independently. I think you have a better shot at them putting all the pieces together. They will learn from the wrong decisions and it will click when they make all the right ones and score their first harvest.