Many years ago in the 1960's when I was flying in the bush in Northern Ontario I used to take my two kids with me in the Beaver on floats when it was a cargo trip.
Both learned to fly the Beaver when they were still so small I had to sit them on cushions, all I had to do was follow with the rudder, when they got bigger they could fly the Beech 18 on floats before they were old enough to start to learn to drive.
If any self serving moron from the Government ever had the nerve to quote the regulations to me about letting someone fly when I was with them I would shove their regulations where they would need an anal scanner to read it.
There that settles that subject.
Chuck E.