1: How do you know the child is "getting training" and isn't already a diver?
2: How you know what depth they were working at?
3: How do you know...
How do you know is a very, very good question, and one that's covered repeatedly in training. How do you know what will happen on a dive and how do you handle it? This question in answered through drilling OOA drills, air sharing, regulator recovery, and other procedures designed to deal with minor problems during a dive. So, you train for instances where you get separated from your buddy, where a regulator first or second stage fails or free flows, etc. You figure if these things happen, no big deal, you're prepared.
Now take away your bc, your tank, your regulator, and any safety/signaling devices in your bc. You are now handicapped in dealing with any otherwise minor problems, not to mention breathing more air due to decreased buoyancy control. Serious scuba accidents happen when problems compound in a series; forgoing basic life support equipment for yourself or someone else is the step towards a series of problems.
Oh heck, you're going to see what you WANT to see anyway... some see flailing arms, out of control people, lack of expertise, etc., etc...
I see a dad who may well be in fairly shallow water and is dealing with the fact that each breath cycle has that much more affect when shallow... I see a dad (?) showing off his kid's skills... I see a kid who's got a weightbelt on... and is trimmed out pretty well... and COMFORTABLE WITH IT. I see a rather 'practiced' Euro-style kiss at the end where BOTH remove their regs... go throught the drill and replace... all without any apparent hesitation, difficulty or other issue. I see a kid who does a nifty 'hand swap' with his reg earlier... in a very relaxed way...
So the presence of a weight belt somehow makes it safe and acceptable? If the kid didn't have a weight belt but seemed comfortable would that make just having a mask and fins okay? Would you, as a DM,
seriously be comfortable leading a dive where one person tells you "I'm just gonna breath of his octo, don't worry we've done this before"? You refer to "their regs ... his reg", but it's all the adults regulator set, if a first stage failure occurs their both out of air; not a problem when each has their own regs and tank. Also, removing your regulator from your mouth shows skill
There's no regulator
recovery drill here and panicked/inexperienced divers seem very good at removing their regulators.
... but, like I said we see what we want to see.
... kinda' like making judgements about what you think you see in a video based on your own perceptions of "what's right"...
You're a Divemaster, when you see a diver who forgets to turn on his/her air in a predive setup and gets ready to roll of the boat do you say to yourself "it's okay, their buddy will turn it on once they realize" or do you tell them "hold on, your air's off" and fix the problem? If you're underwater and someone's regulator free flows, they turn off their air (or run out) grab their buddy's octo and continue diving, do you go over and tell them they should thumb the dive or do you let them continue on without signaling it's a bad idea? Each of these situations puts a buddy team in a similar situation to the video, and despite how good their trim is or how long they've dived, it's still not "right."
Regardless, nothing I say can convince you that their diving is hazardous and wrong. I guess reading through accident reports resulting from buddy separation or equipment failure (when both divers
had their own equipment) wouldn't change your mind either. Perhaps you should mail your certifying agency and tell them ahead of time, "Hey, I'm willing to DM dives with buddy teams where only one of the buddies has a tank, bc, and regulator set; they're shallow dives and everyone's comfortable with breathing off their buddy's octo." If you wouldn't be willing to do this, or if you are but just won't tell your agency about it, then maybe you ought to ask yourself why you won't. If you are, please post the agencies response for us all to read and enjoy.
or is he actually walking 
