Hi Jane, I wouldn't worry too much about this silly book!
The best 'proof' Gerhardt can come out with was the study on babies abandoned in a TB hospital in the 1940s, which (surprise surprise) harmed their mental development!! Yes, exactly the same scenario as putting an under two in a day nursery. Wtf?!
As other posters on the Times website have pointed out, humankind has survived for millenia without having the 'mother as 100% primary carer' type childcare model.
For what it's worth, my nearly 3 year old has been at nursery part-time since she was one, and is very loving, compassionate, and bright child.