A 12 year old with a 3 yo sibling will have 3 years of experience with that sibling and know how to care for them. Of course, if the 12 yo has not been raised t

A 12 year old with a 3 yo sibling will have 3 years of experience with that sibling and know how to care for them. Of course, if the 12 yo has not been raised to be a responsible person, there is a risk. But roughly for millenia, older siblings have cared for their younger siblings while the adults were working / busy. It is a relatively recent development that we don't trust kids anymore.