I can think of some examples in literature - like in "Romeo and Juliet" where the nurse (a wet nurse) played an important role in Juliet's life. And I remember other examples from literature (because they struck me as so odd), especially German where the word for "wet nurse" is "Amme". Often, the child had an even closer relationship with the Amme than with the mother. - But of course, these are just anecdotal examples.