Similar Film

Now here is an off-the-wall question. I recently bought this film, thinking I had seen it before. Unfortunately, while I did enjoy this film, it wasn't the film I was thinking of, and now I'm asking for help.

The movie had a very similar plot, including a brother and sister with supernatural powers. The kids are kidnapped by a rich man. The boy is kept in the barn or stable, and the girl is asked to help the man find uranium. The two kids are attempting to get to a "purple store", where everything in the store is the color purple.

I know this isn't much to go on, but any help would be appreciated.