A girl (no older than 15) living on the Moon or Mars gets visited by her space traveling uncle, who offers to take her with him.
In their travels, they meet and take with them:
- a box-shaped alien with four legs who can change color
- a rusty robot that called out for help with an S.O.S. signal (they later fix him by pouring oil in his articulations)
- a small turtle robot that is decorated with diamonds (which they later discover is actually a robot and either a bomb or a tracking device)
They are being stalked by a bunch of "bad" people throughout the story. It is these guys that gave the turtle to the girl and I think they wanted to capture an alien that traveled with the girl and her uncle.
I had seen this on TV as a cartoon in 1995 or so (was really gloomy and dark). Around 1998 I read this same story in a novel. I am pretty sure the book is older than that.
I've been searching for it for many years now.