That’s why most people make sure it doesn’t happen
Were you not invited to parties in high school? My experience growing up (and my experience being a neighbor to people with teenage children even now) says otherwise.Did you forget what web site you're on?
People, for the most part, have no respect for the law. They usually haven't even read the law. They have respect for what they consider appropriate or inappropriate behaviour. (Knowingly breaking the law is, in most instances, considered an inappropriate behaviour – except copyright law, which people only care about if there are immediately-visible enforcement mechanisms. Basically everyone is fine with copying things from Google Images into their PowerPoint presentations… but I digress.) Most people would object to murder, even if the law didn't forbid it. This distinction is important.
Is there a law that says "children must not play in traffic"? Probably! Haven't the foggiest idea which it would be, though. That law (if it exists) is not why children don't play in traffic. The law against giving alcohol to children (if it exists) is not why we don't give alcohol to children. We can establish similar social norms for deliberately-addictive, deceptive, dangerous computer systems, such as modern corporate social media.
Drawing out the alcohol analogy further, you can actually buy alcohol on Amazon, subject to an ID check. I'm not sure why no one bats an eye at this, but somehow e.g. porn or other adult-only services are different.
It's long been an established, reasonable stance that it is both the parent's responsibility and decision to allow or deny certain things, and it's also illegal for businesses to completely undermine the parent's ability to act as that gatekeeper for their kids.
I'm in favour of this, so long as the restriction is narrow. Children shouldn't be on Facebook, but they should be able to participate in the RuneScape forums under a pseudonym, or contribute to Wikipedia (provided they understand the "no, nothing can be deleted ever" nature of the edit history).
However, most of the things we'd want to prohibit for children, aren't actually good for anyone. It would be much easier, in one sense, to blanket-ban the bad guys: no new accounts may be created on services like Facebook or Discord, unless they change their ways.