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- Graham Oakley - The Church Mice series, Magical Changes
- Robert C. O'Brien (1918–1973) - Mrs. Frisby and the Rats of NIMH, Z for Zachariah
- Jane O'Connor - Fancy Nancy
- Scott O'Dell (1898–1989) - Island of the Blue Dolphins, The King's Fifth, The Black Pearl
- Charles Ogden - Edgar and Ellen series
- Ian Ogilvy - Measle and the Wrathmonk, Measle and the Dragodon
- Jenny Oldfield - My Magical Pony, the Home Farm Twins, the Horses of Half-Moon Ranch series
- Carola Oman - Ferry the Fearless
- Kenneth Oppel - The Silverwing Saga, Airborn
- Pat O'Shea (1931–2007) - The Hounds of the Morrigan
- Uri Orlev - The Island on Bird Street
- Mary Pope Osborne - The Magic Treehouse series, Tales from the Odyssey
- Elsie J. Oxenham (1880–1960) - The Abbey Series
Read more about this topic: List Of Children's Literature Authors