A.A. Milne, the creator of Winnie the Pooh and C.R. Milne (Christopher Robin), lived in the English county of East Sussex on Cotchford Farm where he was inspired to create and write the Winnie the Pooh stories. This was also the last home of the Rolling Stones founder Brian Jones and where Jones drowned in his swimming pool on July 3rd, 1969 at the eerie age of 27 - the same age as Jimi Hendrix, Jim Morrison, Janis Joplin, Kurt Cobain, and many more famous people.
The film is actually fairly accurate in the relationship between Christopher Robin Milne and his parents. However although the film depicts that the older Christopher Robin finally forgave his father for (perhaps inadvertently ) exploiting him to sell the book, in reality C R never actually forgave him the way depicted in the film, instead learning to accept what had happened and to live with it up right until he died in 1996. However his frosty relationship with his father was at least better than the one he had with his mother, not just because of the way he felt exploited as a child but also because she disapproved of the woman CR would eventually marry. After AA Milne died in 1956 he had almost no contact with his mother right up until her own death 15 years later. CR did have one daughter, Claire, from this marriage. Claire was born with Cerebral Palsy and unfortunately died in 2012 aged just 56.
AA Milne was 38 years old and his Wife Daphne was 30 when Christopher Robin was born. In reality Domnhall Gleeson was 33 and Margot Robbie 26 when filming commenced. This also means that Robbie is actually only five years older than Alex Lawther, who plays the adult Christopher Robin.