Factual error: The head master of the school criticizes Belle for "teaching another girl to read." But beginning in 1692, well before the movie is set, all parents in France were required, by royal decree, to send all their children, boys and girls, to school until at least age 13.
Factual error: Christopher Robin and his schoolmates undergo the army medical (which he fails) at the outbreak of war. In fact, Christopher Robin had left school and was at Cambridge by the time the war broke out. In addition, those that pass the medical go off to war in privates' uniforms. As the school (Stowe) is a prestigious public school, almost all would have been commissioned and never served as privates.
Factual error: The family's roadtrip was during "summer vacation", but there was intermittent Fall foliage (yellow, orange, red leaves) during their four days traveling. Quite often, the foliage was closer to what would be expected in late September or October and even November.
Factual error: "Colonel" Roderick has incorrect rank insignia on his collar. Looks like Sergeant First Class (three above, two below).