You could verify the ID of an adult who vouches for the child they are a legal guardian of. That way, if it turns out that Brayden(M12) is actually Linda(F45) you know who to send law enforcement to to ask some very pointed questions.
That said, I don't think online ID verification is effective and even if it was, it wouldn't be worth the level of mass privacy invasion. If your goal is actually to help kids who are victims of abuse, your efforts are much better spent elsewhere. For example: making child abuse report hotlines/websites more easily accessible and widely known, fixing social services so that they actually provide better help when requested instead of making things worse, better education for children about what is and is not OK behavior even from "trusted" adults, and how to get help from someone who isn't a relative when you need it. "Stranger danger" hysteria catches all the outrage and public discussion, but is the least common source of abuse.
The parent will input the real birthdate of their child, or it's their responsibility if the child encounters anything not age appropriate.