When Aidan was born, everyone thought he was a girl. His parents gave him a pretty name, his room looked like a girl's room, and he wore clothes that other girls liked wearing. After he realized he was a trans boy, Aidan and his parents fixed the parts of his life that didn't fit anymore, and he settled happily into his new life. Then Mom and Dad announce that they're going to have another baby, and Aidan wants to do everything he can to make things right for his new sibling from the beginning--from choosing the perfect name to creating a beautiful room to picking out the cutest onesie. But what does "making things right" actually mean? And what happens if he messes up? With a little help, Aidan comes to understand that mistakes can be fixed with honesty and communication, and that he already knows the most important thing about being a big brother: how to love with his whole self. When Aidan Became a Brother is a heartwarming book that will resonate with transgender children, reassure any child concerned about becoming an older sibling, and celebrate the many transitions a family can experience.