Ok, I remember watching this animated movie in early 2000 I believe, it’s in english, Pretty sure it’s a movie. But it could be an episode thing, Bascially, the movie is based on halloween, and a boy and his friends all go trick or treating, but he has to bring his sister along too so he’s all grumpy about it, and so they go to this haunted house like place and they trick his sister into going inside and they lock her in, and then she meets all these friendly monsters etc. I think it’s animated. 🙂
Sounds like Scary Godmother. Here’s the imdb link
http://www.imdb.com/title/tt0330859/?ref_=fn_tt_tt_3
and the video