The US generally has strict anti-alcohol laws, with exceptions for legally-recognised familial relationships (e.g. children, spouses). The UK doesn't: its laws are restricted to "the relevant premises" (https://www.legislation.gov.uk/ukpga/2003/17/part/7/crosshea...) and "in public" (https://www.gov.uk/alcohol-young-people-law – can't find the actual law right now); but still, the behaviour I described does not occur in the UK often enough for me to have heard of it. I have, however, heard about similar behaviour from the US, where "we all go out late at night and become alcoholics" seems to be a culturally-acceptable form of teenage rebellion.

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.

We can establish social norms, but companies have a tendency to ignore those norms if it makes them money and it isn't illegal (maybe not all or even most companies, but if it's profitable, some company will do it and expand into that niche). So it makes sense to make it illegal for those companies to provide services to children, and then establish a social norm that parents won't create an account for their children/bypass the checks that companies need to do. Just like with alcohol: it is illegal for stores to sell it to minors, and they must check ID; we don't just let them shrug and say a 14 year old looked 21, and at least in the US, that would be a criminal offense. It's then socially unacceptable (and maybe also illegal) for a parent to buy a ton of alcohol so their kid can host a rager for all of their friends.

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.