>> I suspect this is not just an American or British or solely cultural thing but also a number-of-children thing. This seems like it would also be the natural

>> I suspect this is not just an American or British or solely cultural thing but also a number-of-children thing. This seems like it would also be the natural response to having fewer children. I suspect the same. When the first child is born, parents tend to be extremely protective of them. By the time 3rd, 4th is born, they are in "been there, done that" mode. Further, by the time the 3rd and 4th kids are born, the older ones are already starting to take up some responsibilities. That includes, rearing the younger siblings. Note: Not talking about graphs or trees