The parents are clearly frustrated fuckwads who have "discovered" a "loophole" in which they can torture their children under the guise of "pranks". It's not like they genuinely believe these are pranks, but they have effectively given themselves an excuse to abuse their children.
You can clearly tell the parents are beyond frustrated. They constantly blame the kids and insist its their fault, in the middle of their abuse sessions they always yell and curse at their children for being "terrible", for "not valuing their stuff", for "taking things for granted". I know this is steering well into the armchair psychologist territory, but if I were a betting man I'd put my money on these fuckwads being failed, frustrated parents who have figured out a "creative" way to take their anger out on their kids.
Their audience consists of fucked up assholes who genuinely enjoy seeing children getting abused. There's that one screencap of one of his subscribers admitting to it: they know the kids are getting abused, but they enjoy seeing kids abused, much like some maladjusted asshole enjoying torturing animals. The failed parents see their success in YouTube as validation: if what they were doing was so wrong, how could they be so successful? And, much like any bully, they pick on the one kid who has the "best" (read: most psychologically damaging) reactions.
This environment isn't healthy for any kid. The parents have completely given up on their job. You can tell that they're not just doing this for the money: they genuinely enjoy seeing their kids beaten, they enjoy yelling at and cursing at their children, they enjoy blaming them for their parenting failures, and they feel perfectly comfortable framing this as a "prank", not because they genuinely believe it's a prank, but because they can use something as an outlet and excuse for their abuse.
Armchair psychologist again: I imagine the very first child abuse video they put up as a "prank" was some form of catharsis for them to blow off their anger as failed parents. Then they saw this was by far the most popular video they had ever uploaded, and proceeded to go again, and again, their views and audience increasing each time, and their own personal enjoyment of torturing their children increasing each time. They managed to figure out some fucked up way to turn their frustations at seeing their own kids crying, angry, and hateful toward them into a form of pleasure. They're going scorched earth: "if my kids are unhappy because I'm a monumentally shitty parent, at least I'll get some fun out of willingly abusing them. They would've been unhappy anyway, and hey I'm making money off this!"
These parents are monsters and are no longer parents. They're no longer interested in raising their children. They're objects to be used for their pleasure, they're outlets for their anger, and they're assets in their money-making scheme. They only care about them enough to ensure their freakouts and mental breakdowns are more explosive.