APA (7th ed.) Citation

Galan, A., Galan, A., & Simpson, S. (2009). Billy Bully: A school-yard counting tale. Cartwheel Books.

Chicago Style (17th ed.) Citation

Galan, Alvaro, Ana Galan, and Steve Simpson. Billy Bully: A School-yard Counting Tale. New York: Cartwheel Books, 2009.

MLA (9th ed.) Citation

Galan, Alvaro, et al. Billy Bully: A School-yard Counting Tale. Cartwheel Books, 2009.