What are some examples of how family is generally presented as a theme in confessional poetry?
Two of the most prominent confessional poets would have to be Anne Sexton and Sylvia Plath. Sylvia Plath's poem "Daddy" could certainly apply to your theme of 'family.' Although her poem does not paint a very nice portrayal of family life, "Daddy" would give you a wealth of information and examples for your compare and contrast analysis.
Another Plath poem about family that shows an alternate perspective is her poem "Morning Song," which she wrote after the birth of her first daughter:
The midwife slapped your footsoles, and your bald cry
Took its place among the elements.Our voices echo, magnifying your arrival. (1-3)
Plath does not sugar coat the birth of her daughter, but rather shows the event plainly, austerely even. "Morning Song" shows Plath's pragmatic approach to motherhood, entrenched in sort of a realist approach.
Plath's non-sentimental stance on her own experience with motherhood could also be contrasted nicely by yet another poem about her parents, this time her mother, "Medusa." It does not take much imagination or even deep literary analysis to draw some conclusions about how Plath felt about her own mother based solely on the title of the poem!
Plath's rich confessional style poetry gives the reader contrasting views on love, family, and parent-child relationships.