Factual error: Allegra was said at the end of the film to have died aged 10. She was actually 5 years old when she died.
Factual error: In the movie the professor's assistant says thst the professor was in OSS in the great war (WWI). OSS was first formed in 1941 by President Roosevelt.
Continuity mistake: While Jim is narrating his story, he gets to the point when his son was hit by a drunk driver. The line slows down, but when it cuts to a close-up of Renée Zellweger saying "Sorry Jim", you see the trays shift. Only, they are back in the exact same spot as before when the close-up is over. (00:28:20)
Factual error: The musicians in the (real) Band of the Coldstream Guards that plays Happy Birthday for Christopher Robin are wearing their 21st-century uniforms and medals.
Factual error: The film describes the British headquarters in Kenya as the "British Embassy." Kenya was still a colony, so there was no British embassy; it was Government House.