Who is Peter from Back When We Were Grownups: A Novel and what is their importance?

Peter is Rebecca's step-grandson, the son of NoNo's new husband Barry. When we first meet Peter, he seems as discontented with his life and circumstances. Over the course of the narrative, however, Rebecca's consistently fond, and occasionally outspoken, attentions thaw Peter's resistance to her, to the point where he even asks her to be a surrogate grandmother on his Grandparents' Day at school. Rebecca's blossoming relationship with Peter makes her life worth celebrating