Yes, platforms do need restrictions—but not implemented from that direction. The correct approach would be to block all content that is not suitable for children by default.
Other content should only be accessible after age verification.
This means children would not need to verify their age. Instead, adults who want to access restricted content would need to verify that they are of legal age.
We should not implement systems that find or track children online.
That idea is fundamentally misguided, and no one will convince me that it is reasonable.