When and where was the author of The Twenty-One Balloons born?

Sine the 1947 novel Twenty-One Balloons does not concern an author, and is instead the tale of a retires schoolteacher, I assume you are asking about the author of the novel.

William Sherman Pène du Bois was born on May 9, 1916 in Nutley, New Jersey. Nutley was incorporated as a township shortly before du Bois' birth, having formerly been Franklin Township. He was born to a mother who was a children's fashion designer and a father who was a well known painter and art critic with a focus on landscapes and portraits. Du Bois spent his formative years in France, where he received an education at the Lycèe Hoche at Versailles before returning to Nutley and attending an American high school.