I recently read Mother Nature, by Sarah Hdry, which is a totally fascinating book and one I highly recommend for anyone interested in motherhood, babies or parenting. It will challenge pretty much every assumption you had about these topics: for example, humans are innately rather bad parents and the risk of being abandoned (or killed) at birth has apparently been a major driver in human evolution. So much for "natural parenting"!
One of her main arguments has to do with "alloparenting". Human babies being the almost ridiculously helpless, needy creatures that they are, it is basically impossible for mothers to raise them alone (unlike, for example, bears). Instead, they make use of alloparents, who are non-mothers acting in a maternal role: stand ins, if you like.
The problem with alloparents, though, for mothers in every era/culture, is that it is very difficult to find good ones. It is the rare non-family member who is willing to provide the careful, responsive, personalized affection necessary to properly raise a human being. (This is why most alloparents are in fact close relatives, particularly maternal grandparents: and may even be one reason for the striking longevity of human females post-menopause.) Note that this isn't because non-relatives can't: they just, by and large, are not motivated to do so.
It made me think differently about childcare. I wrote before about how sending children to daycare, even at very young ages, does not necessarily seem to have negative effects. This isn't surprising if human infants have evolved in an environment where multiple caregivers might be involved (up to dozens, for certain close-knit hunter gatherer groups in central Africa).
But for successful outcomes, these other caregivers must have the status of alloparents: basically mother-figures, with the passionate love, continual involvement into adulthood or at least late childhood, and absolute loyalty than this implies. By involving someone else in daily/very frequent care of your child, you are therefore not just hiring a babysitter, you are adopting a member of the family (almost literally).
Daycare is no longer a convenient place to leave babies/children, but truly their second home. If parents don't treat it that way (by frequently switching situations/caregivers, not developing a familial relationship with caregivers), then children are likely to suffer from a whole host of psychological, emotional and even physical problems. Makes me look at sending R to preschool in a whole new way!