Probably something to do with a mixture of less parental time and less money available.
I was from a family of 5 children. I think we had a lot more freedom than children these days. Parents did not obsess so much over children being away from home because they were so busy, they did not have time to worry, also there was very little traffic. We wore a lot of "hand me down" clothes from relatives. The children learned a lot from their older siblings and other children (not always what they should have been learning, mind you).
Children are in smaller families these days and often there is more pressure on them, for instance to take music lessons, go to drama classes, etc. they may get a LOT more parental attention, which isn't always necessarily good. Many kids these days are dressed in designer clothes! they dare not get dirty. We were in old clothes and had no problem getting dirty, climbing trees and generally being kids.
The kids that were from smaller families, even in my young days, had more parental attention. My own mother once confessed that she probably thought that we thought we had been neglected! But I assured her that it had not felt like that to us. I think that children from smaller families expect to have more done for them, they seem often to be very dependent on others doing things for them. They do not appear to me to be as independent as those from larger families who had to do more for themselves.