In April, Melanie Notkin, a social-media entrepreneur, seized on this underrepresented underclass with “Savvy Auntie: The Ultimate Guide for Cool Aunts, Great-Aunts, Godmothers, and All Women Who Love Kids” (William Morrow). Her book is a spinoff of her Web site, savvyauntie.com, which aims to be an “all-inclusive guide” for what she calls PANKs: Professional Aunts No Kids. It’s a rallying girl-call in high chick-lit style: lots of hot pink and cheerful advice filed under rubrics like “Auntre-Nous: Straight Talk for the Childless Auntie” and “The Importance of QualAuntie Time.”