Free speech in Europe is under serious attack.
Why not produce a second kind of phone that is for kids. Maybe have it linked to their parents accounts on a hardware level. The kidphone is physically restricted somehow to only installing certain apps, so that parents can ensure they are safe.
This approach would put the power back into hands of parents, keep the kids safe, and also prevent all this intrusive age verification stuff from happening.
Also it is a lot easier to police. You could physically look at the phone the child is using to make sure it is a kidphone. If not, then they are committing a crime, similar to a child smoking a cigarette.