I find the connection between income level and child development interesting. When income levels are low, children may be malnourished or may not be cared for as well and this will definitely affect their emotional development negatively. But I don't understand how else income affects emotional development.
Families with very high income may also be working a lot and may not spend much time with their children. Or they may hire nannies to care for their children and not bond with them as much either.
So I don't think that it's very accurate to say that children of low income families have poor emotional development.