Note that in reality, all parents are experimenting. Nobody _knows_ the right way to raise a child. I'm the father of a 3yr daughter but I dare not claim that my way is the right way...

They can't give consent to what they eat, when they go to bed, where they live/vacation, when/whether they see a doctor, whether they are vaccinated, whether their caregiver drives obeying all traffic laws/not drinking, etc, either.

I believe that parents (/guardians) have responsibility for the children and that responsibility logically extends to giving consent for choices like this. My mother performed "experiments" on me in conjunction with her master's degree work in education; I was probably 8-10. It was clearly her call; I couldn't give fully informed consent, but there wasn't any risk of physical harm and vanishingly small risk of any possible harm, so I believe her consent by proxy was appropriate.