The Little Vampire (2000) - Rotten Tomatoes
It is not easy being a 9 year old in a new country. Tony has just moved with his parents, Dottie and Bob Thompson, from a big bustling city in America to a small village in a remote corner of Scotland. Every night, in his new home, Tony has nightmares about vampires, and he has no idea why. He soon becomes so absorbed by them that he starts studying every book he can find on the subject. His classmates tease him about his vampire obsession, especially the cruel local kids, Nigel and Flint, nephews of local squire, and Bob's employer, Lord McAshton. The teacher at his new school is so shocked he tells Tony's Mom about how worried he is; not a good start for the new kid in town. One evening, while in his room, practicing basic vampire moves, Tony gets a visit from a large bat, which transforms before his eyes into a 9 year old vampire boy, Rudolph, who happens to be extremely hungry, and convinced that Tony is one of his kind.
https://www.rottentomatoes.com/m/little_vampire