Ask via hand signals plus watch for any signs of distress (I did not see any signs of distress from the kid in the video - in fact it looked like he was having fun rather than being abused.)
Watch for bubbles, especially on ascent.
Basically the same question unless Dad totally fails to monitor the gas supply. But assuming they are shallow (lots of color in the video under what appears to be ambient light) they they do a swimming ascent. Practically speaking I have never had a failure to deliver gas reg failure in over 20 years of diving, many of those years with well over 100 dives per year.
The same thing that happens if dad has a massive coronary on the interstate on the way home. Lets get real here - kids are risk of accidental death when a parent checks out in lots of environments. Shoot...if mom smokes and falls asleep on the couch with a cigarette, the kid could be doomed in the resulting fire (an event that recently happended locally). We don't automatically brand all smokers as child abusers or reckless endangerers.
Personally, having dove for over 20 years spawned 2 divers and not having any kids die on my watch, I don't think doing what is in the video is any more dangerous than many other "normal" sports soccer moms haul their kids to every day. Soccer being one of them - current research indicates a high incidence of traumatic brain injury in soccer both from getting whacked in the head and also from bouncing the ball off your own noggin.
Is their some risk? Absolutely, but the odds are probably still greater that the kid will get hurt on the drive home. There are however benefits. The kid is interacting with Dad, he is not playing video games, and he is probaly developing a love for diving that will keep him intersted, occupied and academically attuned to relevent subjects during his teen years in high school. All of which will reduce the risk of other types of high risk drug and alcohol related behavior later.
In my former Child Protection Social Worker opinion, as long as Dad did a proper amount of pre-dive briefing and education and proceeded cautiously and incrementally, I see no evidence of abuse. I'd still be more upset with the ignorant soccer mom who is blissfully ok with her kid knocking the ball around with his or her head.
Excuse me while I go put on my nomex suit....