Everyone walks to August's house for cake after the reception. August hears the Star Wars hero music in his head and feels ridiculously happy. He watches Dad telling other adults a funny story and then notices that Mom is hanging back from the group. She looks happy, but August steps back and puts an arm around her. August thanks her for making him go to school, and Mom thanks August for coming into their lives. She calls him a wonder.
When August steps back to make sure his mom is okay, it suggests that he truly understands now that adults need love and comfort, just like kids. By offering this to his mom, he shows her that he's not going to abandon her just because he's growing up and becoming more independent.