F-Droid isn’t the only one: I also like Neo Store, which has more than just the F-Droid repository and I think has a better interface. However, I think not all repo are 100% safe because F-Droid verify all the apps they have while Neo-Store doesn’t because it simply list known repos, which you can activate however you like in the settings.
You have to give them a reason to get interested in the OS and the programs they’re using. I gave Linux a try because I was concerned about privacy and I wanted to use more ethical and user respecting OS and software than what I used at that time. Linux and the FOSS world was an obvious choice for me. Custom ROM on Android was sort of the bridge which allowed me to transition. If it wasn’t for that, I would still be on Windows and I wouldn’t learn that much on how an operating system works and what differentiate them, aside from the look. The fact they’re kids or that they play games have nothing to do with it: a lot of adults don’t know either what type of OS they’re using, despite it being in their best interest. The problem is that we don’t give or show them the reason they should be interested, or at least be curious about it and most of time, before people get a degree, we end up killing their curiosity.
As they play Minecraft, you can advise them to switch to Prism Launcher instead of the minecraft launcher, especially if they mod the game, it’s much better for that. It could be a good start.
Honestly, I think it’s great: if it annoys people enough, they will move out from Chrome and install Firefox (or one of its forks) with good extensions for blocking ads on YouTube. It seems to be the only solution to break the monopoly of Google on browsers. So go Google, I believe in you!