ISPs and OSs should be the ones providing these tools and make is stupid easy to set up a child's account and have a walled garden for kids to use.
There's a law going through in some state that want's to do this, but also put the onus on the OS developers to detect age aligned behavior. How do you do this with Linux? It would kill the open computer and kill ownership over computing.
Mark Zuckerberg advocates for this, most people entrenched in this argument think it's worse. But I'm all for burning it to the ground so.
You must not have kids if you think it's easy to keep children off things that are bad for them.
I live in the UK. By default your ISP will block "mature" content and you have to contact them to opt out. iOS, Android, Playstation, Xbox, Switch all have parental controls that are enforced at an account level.
A child with an iPhone, Xbox, and a Windows Laptop won't be able to install discord unless the parent explicitly lets them, or opts out of all the parental controls those platforms have to offer.
The tech is here already, this is not about keeping children safe.