As far as I can see, this research proves nothing about about working or not working, nurseries or not nurseries, but what it does say is children of fulfilled stress-free mothers are less stressed than children of stressed mothers. (and presumably sahkids of happy fulfilled sahms are less stressed, too!)
Durrrrrrrr.
I think the contributors to MN should set up a research project to find out what we all know, and WE should get the fee!