Frog was one of the children in the Sewer King's child-slavery racket.
Frog was rescued by Batman after nearly being hit and killed by a subway train. He was brought to Wayne Manor and looked after by Alfred Pennyworth, who had difficulty with the boy. When he was caught fooling around with an antique gun, Batman realized how serious Frog's situation was, and asked him for help.
Frog led Batman to the Sewer King's lair. Once the Sewer King was apprehended, Frog and the rest of the child slaves were freed.