While not specifically about Frankenstein, Dracula, and a werewolf, it's a popular kids' movie with a cast of classic monster characters:
* Dracula is the main character, running a monster hotel.
* Frankenstein's Monster is a lovable guest at the hotel.
* Werewolf is a recurring character, and his son is a key part of the story.
There are also several sequels, with the monsters getting into all sorts of wacky adventures.
It sounds like you might enjoy this series!