"isn't actually".
It's dual use. It is about protecting children, but also along the way these other properties happen to come along. Thing is, with enough cryptography, we could get a way that this would work, but it's too complicated, which results in you being right after all.
> with enough cryptography we could get a way this would work
No amount of cryptography will stop a parent from handing a verified device to a child. Parental controls (however effective you think they might be) have come enabled by default in the UK for the last decade and literally need to be turned off - which is exactly what will continue to happen.