I think most PBs have an SEL component, but no one pointed it out before. How many books deal with making a friend or overcoming a fear? How many have someone standing up to help someone else or showing resilience or learning to adjust a message to the needs of an audience? How many are about learning to share or love yourself for who you are? All of these are SEL topics. They include the earliest PBs, the classics, and books of today.