However, this is not about age verification or protecting children. That is just the excuse they are using.
If Meta, Google etc could easily have algorithms in place for determining the age of the person seeing the video - apart from having the override capability via a parental login as you have stated.. but these platforms have consistently refused to limit the type of content they are showing to children.
YouTube has this. It’s YouTube Kids. You can argue all day over whether it’s good enough but they do have this offering.