Have you considered the possibility that children actually don't acquire their values exclusively from their mothers? But rather, acquire them from their interaction with the culture at large? Have you considered the possibility that, just for example, schools are sites of sustainable transmission of values between the children themselves? So that kids end up learning a very large chunk of their values from peers and kids slightly above their grade.
This is the central argument of an excellent book called The Nurture Assumption by Judith Rich Harris.