I would add not everyone shooting correctly, aiming with their dominant eye can shoot with both open.
Tell me more.
My brother and I learned to shoot in our basement with air guns. We were 8 and 10 and both left handed. Dad a navy vet shot military match rifle and bullseye pistol and shot with one eye closed. He instructed both of us to shoot with 2 eyes and my brother could never get the hang of it. I just kind of willed myself and 45 years later it is the only way I shoot (even scoped rifles).
The second image of the non-master eye was to much for my brother to ignore, and once it became habit it was to late for him to change. In my experience shooting a lot both at home in the basement and once I got older weekend skeet and trap shooting made both eyes open instinctive. I will say that I never had any issues with my eyes changing dominance. I am left handed eye and hand.
Also some people gravitate to the wrong shoulder due to comfort rather than eye dominance. My youngest son took that route and no amount of coaching could make him change. He shoots left handed with his right eye closed. I knew his dominant eye was his right but he found shooting right handed to uncomfortable and my attempts to convince him otherwise failed. The only reason I continued is I didn't want him to lose interest and the vast majority of shooters I know shoot with one eye.
I think once a youngster is both strong enough to hold a gun and recognizes their master eye practice has to be frequent and fun in the beginning. Create good habits early and if you hit a brick wall stop. Perhaps a better coach could have persuaded my son. Especially to at least shoot right handed, shooting left handed if you don't have to opens more options.
I should have mentioned when I wrote this originally that sometimes we start them to young. I'm not passing judgement on anyone here but its better not to have to unlearn a bad habit. An older child who understands what they are being shown and who then is given plenty of opportunity to practice correctly will be ahead of the curve.