Aaron is the son of Kirk and Francine Langstrom,  however due to Kirk's serum turning him into man-bat, he was born with a bat like appearance. As a child he was kidnapped by the villainous Jaeger, but was defeated by Man-Bat with assistance from Robin, with Aaron being returned to his parents and sister.  While his father works to give his son a way to shift between his humans and manbat form.
 
Later, hearing his parents in a heated argument over whether or not to ask Bruce Wayne for help with Aaron's condition, the boy leaves to go ask him for himself. After arriving in the Batcave he stays there for several months without alerting anyone to his presence. Aaron is eventually discovered, when his father arrives looking for him, where Bruce agrees to help if Aaron brings back the bats that had abandoned the Batcave after being vaccinated against the clench virus.