Although he was officially named Christopher Robin, his parents often referred to him as "Billy". When he began to talk, he pronounced his surname as Moon instead of Milne. After then, his family would often call him "Billy", "Moon", or "Billy Moon" instead of Christopher Robin. In later life, he became known just as Christopher.
On his first birthday, he received an Alpha Farnell teddy bear he called Edward. This bear, along with a real bear named "Winnie" that Milne saw at the London Zoo, eventually became the inspiration for the character of Winnie-the-Pooh. Edward the teddy bear was about two feet tall, light in color, frequently losing his eyes, and a fairly constant companion to Milne.
As was customary for upper-class and upper-middle-class children at the time, Milne was reared by a nanny. Meetings with his parents were restricted to short periods just after breakfast, at tea time, and in the evening, just before he went to bed. As he grew up, he spent more time with them; however, the Milne parents spent little time together, forcing their son to divide his own time between his mother and his father.
Time spent with his father led to Christopher Milne's love of mathematics and cricket, as well as to their shared pacifism. Though Christopher greatly underestimated his intellect, referring to himself many times as being "dim", he was extremely smart for a boy of his age. The reason for his denial of his intelligence was that he was able to solve complex equations with little or no difficulty but had to concentrate on much simpler ones.
From his mother, Christopher Milne acquired a talent for working with his hands. He owned a small tool kit, which he used to take apart, and then reassemble, the lock on his nursery door when he was only 7. Milne's other achievements with his tools, accomplished by the age of 10, included modifying the works of a grandfather clock and altering a cap gun so that it would shoot real bullets.
Milne first attended the Gibbs School, an independent school in London, in 1929. From Gibbs, Milne went on to Stowe School, an independent boys' school in Buckinghamshire, where he learned to box as a way to defend himself from the taunts of his classmates. In 1939, he won a scholarship to read English at Trinity College, Cambridge.
Although Christopher had previously had a close relationship with his father , this bond was broken by his war experience. While serving abroad, he began to resent what he saw as his father's exploitation of his childhood and came to hate the books that had thrust him into the public eye. After being discharged from the army, he went to Cambridge to complete his studies and graduated with a Third Class Honours degree in English.
On 24 July 1948, Christopher married his first cousin, Lesley Sélincourt. His mother Dorothy (née de Sélincourt) disliked the marriage, partly because she did not get along with Lesley's father, Aubrey de Sélincourt, the classical scholar and translator, who was her own brother. (Dorothy had wanted Christopher to marry his childhood friend, Anne Darlington.) In 1951, Christopher and his wife moved to Dartmouth to found the Harbour Bookshop, which turned out to be a success, though Dorothy had thought the decision very odd, inasmuch as Milne didn't seem to like "business" and, as a bookseller, would regularly have to meet Pooh fans. While both of these factors did cause them frustrations, Christopher and Lesley ran their bookshop for many years without any help from royalties from sales of the Pooh books. Christopher occasionally visited his father after the elder Milne became ill, but once his father died, he did not visit his mother during the fifteen years that passed before her death.
A few months after A. A. Milne's death in 1956, Christopher and Lesley's daughter, Claire Milne, was born and was diagnosed with severe cerebral palsy. Claire runs a charity for the disabled called the Clare Milne fund.
In 1974, Christopher Milne decided to publish the first of three autobiographical books. The Enchanted Places gave an account of his childhood and of the problems that he had encountered because of the Pooh books.