I used pretty much the same set up to begin training my young sons at the age of around 8 yrs old. Other than not blowing bubbles from the mouth when the reg was out, what problems were observed?
Is it necessary for a child to wear his own tank and BC? I used a 6-ft hose for my kids and they pretty much were under my arm or holding my hand when we were swimming. In some respects the child is easier to control when he is dependent on you for air. Not having to mess with the tank and bc also provides some benefits in my mind.
The only real additional danger that I see is that if they have a first stage failure, then they don't have a redundant system to share.???
I'm no expert, but I'd say the obvious problems were quite enough. Mainly...
1) No redundant air supply (Okay, sure, the photographer might have been able to help, but if the "instructor's" system fails, there would then be THREE divers breathing off the photog's system)
2) This seems to be at "significant" depth. The color has a blue cast, and the reds and pinks seem to be quite muted, so I'm guessing at LEAST 20 feet. While this isn't too tough for a trained adult, it might be a problem for a child should they have to bail. And what are the chances that the kid WOULDN'T hold his breath on the way up?
3) The child seems to be overweighted. When the two start swimming, the child's trim is definitely above horizontal, indicating too much weight (but then, the same is true for the adult). To me, negative buoyancy could pose a real problem in an emergency situation.
4) Sure, the kid doesn't blow bubbles during reg removal...neither does the "instructor". This implies that the adult is barely capable of the skills necessary for safe diving, much less teaching.
At best, this is a very marginal situation. At worst, it's a disaster waiting to happen. (but that's just my two pennies' worth)