They cannot adjust odds of the slots, that's not how that works. The casinos can cover any losses of slot streamers however.
Also why does this "children" thing keep coming up? Casinos don't want children to play their games, they don't even have money to spend!
I am a head of operations in an online casino. I am responsible for gameplay provider integrations, psp integrations and many things more.
The slots rtp is absolutely set by the game play providers, even the aggregators just pass it on. It is not configurable in any way, not on user level, not on casino operator level, it is always global scope.
The game play providers earn by rev share, they are the top of the food chain and it would be economical suicide to provide different APIs, they have some settings depending on some GEOs, but these are things like no auto play, stake limits etc.
Any regulated casino is using these, the audience is not naive, of course, there are some fly by night operators using pirate games, but this gets detected fast and is often the reason for these casinos having bad rep online, amongst affiliates who will not have them listed etc. These are operated by incompetent people.
From a technical perspective, even if we assume that the operator indeed can’t adjust the odds, it would take an engineer only a few hours to mock out the API endpoints the front end calls to return consistent wins and then it’s just a matter of using a browser extension or a proxy to redirect all traffic to the fake server to be able to film such a video (still much easier than faking the video itself).