I'm not the parent, but from my pov FB is a net negative for society, so if they are unwilling to play by our laws, then I'd rather see them get the fuck out.

They won't of course, because it leaves the market open for grabs.

If they leave the EU though they don't need to follow European laws or pay European taxes, but that doesn't prevent European users from continuing to use the actual website.

No, that's not true.

Due to trade agreements US companies have to follow EU law, for EU citizens, even of those companies don't have a presence in the EU.

In other words Facebook would have to block EU users.