What is this movie called?

[lweihrnwer]

I watched the movie a few years ago, so I'm assuming it was either made in the 90s or early 2000. I need some help finding the title. I think it was a horror movie, it starred 3 (or 2) kids, two boys and a girl who entered some portal with their parents. (I can't remember what goes on until the end of the movie). But I do remember that over the course of the movie, duplicates of the parents are made and at the end, the kids finally find their parents and drive their station wagon though a portal, but at the (daughter or son's) birthday party (?) the parents are revealed to be copies as they cut cake and goo comes out of their mouths. The daughter sees this while dancing and ends the movie by screaming.