Otis (pen name) was noted primarily for his authorship of scores of children’s stories which included the very successful Toby Tyler. Toby Tyler is about an orphan who runs away to join the circus, but, realizing his big mistake, tries to earn and save enough money so he can go back to his foster home. This book was extremely popular, and for the rest of his life Kaler published many children’s stories, a few of which were Stories of American History, nine of the eleven books in  the Minute Boys series (the remaining two were written by Edward Stratemeyer), Continental, Young Patriots, and the Pioneer and Home Life of the Colonists series in which Mary of Plymouth, a story of the Pilgrim settlement, was written.

Under his pen name, Otis, Kaler also edited works on American history. Amy Prentice became his pseudonym for books he published for juveniles.