Currently my kids got already out of my hand, and I really wonder how could I filter the content that goes to them. Internet became something else, so maybe I won't install a VPN to their phones and they won't be able to see the most horrible things anymore.
What is your source? I believe you are incredibly biased. Netflix is one of the biggest user of bandwidth worldwide, and if we're talking about the percentage of "pornographic" IP packets, I think it's even less than the former.
> and I really wonder how could I filter the content that goes to them
Parental control on device and DNS-level blocker (think AdGuard, PiHole, ...). Hosts file could also work as long as they're not admin on their PC. If they're skilled enough to circumvent all of that, then I think your kids will be fine.