Yeah, the First Amendment applies to children after all. We shouldn't give the government, tech companies, or even parents total control over children's online communications. The only exception is when they're very young, and even that should be actualized locally by parents rather than the online platforms or the government. I think a good test for maturity is whether they're able to purchase and use their own device. If the kid can figure out how to earn 100 dollars and buy a used phone off of Craigslist without your guidance, then it's time to let go or at least loosen your controls from device-level to the home router level. And when they can afford their own mobile data or figure out VPNs that can't be blocked by the filtering you set up on the router, I'd say they're ready for the open Internet.