Age checks are only for minors. Parents have full control over their children's devices. If they wanted to, this could all be done without any new legislation - the EU makes some easy-to-use filtering software (whitelist, blacklist, time limits, etc.), parents can (if they want to) install it on their children's devices (it could even come preinstalled, with sensible defaults, since we can all agree on what is "harmful content"), and voila - the child is "protected".
That they instead chose to expand surveillance [1] tells me they have ulterior motives.
[1] They claim it'll be privacy-protecting. I'll believe it when I see it.
https://archive.is/Htwxm