Nothing to See Here by Kevin Wilson is summery and heartfelt and so funny, about nannying your ex-best friend's twin stepkids who spontaneously combust. The Pleasing Hour by Lily King is a solid summer book to me, too, about an au pair in France, but maybe on the sadder side of the spectrum at times. I'd also throw in Commonwealth by Ann Patchett which has a few traumatic moments but is overall a superb read about the children in two families who spend summers together in Virginia, and how their lives change in adulthood, and it goes back and forth between the two timelines
