This doesn't make sense, the population has only increased.
Quick Google tells me 40 years ago, in 1985, there was 62.6 million children in the US. In 2025 there are 74.7 million. That is more children in 2025 than 1985.
Parents not allowing their children to play independently isn't due to lack of other children, it's a choice.
I suspect the number of children born to the kind of parents who's kids six figure white collar professionals want their kids in contact with has gone down.
Quick Google tells me 40 years ago, in 1985, there was 62.6 million children in the US. In 2025 there are 74.7 million. That is more children in 2025 than 1985.
Parents not allowing their children to play independently isn't due to lack of other children, it's a choice.