There was a book (series?) that one of my teachers was reading to the class when I was in school (I want to say around grade 4) back in the mid 90's. It's killing me that I cannot remember the name of it.
I do not remember much about the story, but hoping what I do remember can give some clues.
I remember the story involved a brother and a sister, and some form of space travel not involving spaceships. From what I recall the brother and sister accidentally traveled through space, and got separated. Then my memory blurs, but sometime after that the girl character is touring what is essentially an alien "zoo", where she finds her brother is one of the "exhibits". Some of the dialog I remember, is the alien tour guide was describing her brother (though she did not tell these aliens they were related), and how they had incredible difficulty in trying to create a habitat for this "creature" (the brother), but they were very surprised when the brother created his own habitat (he constructed some sort of house or hut). I believe there was a quote similar to
"It built it by itself!"
Other than that, I don't really remember except that I think this story was part of a series, and that the main premise of the story was the kids trying to find their way home.