Lottie And Lisa by Erich Kästner
The book tells the charming story of identical twin sisters separated at birth who meet unexpectedly at a summer camp. Initially unaware of their relationship, the girls take an instant dislike to each other due to their identical appearances, but as they get to know one another, they discover their shared parentage. They decide to switch places, with each going to live with the parent the other has grown up with, in an attempt to reunite their estranged family. Through a series of heartwarming and humorous events, the twins work together to bring their mother and father back together, exploring themes of family, identity, and the bond between siblings.