At the very start of the movie a pencil is being sharpened with a knife, which is accurate for the period, however, when the pencil is taken from the box, before sharpening, it has clearly been sharpened with a modern pencil sharpener.
In the film the book "The Tale of Jemima Puddle-Duck" is shown to be published followed by "The Tale of Two Bad Mice" then "The Tale of Mrs Tiggy-Winkle". In reality "Two Bad Mice" and "Tiggy-Winkle" were released in 1904 and 1905 respectively and "Jemima Puddle Duck" wasn't published until 1908 with five other books in the intermediate years.
In the railway station scene filmed on the Bluebell Railway, the LNWR on the tank locomotive has been very visibly altered from LWSR. The N stuck over the W is a really bodged job for such a close up shot.