Cartoon movie set on mars, human kids with alien pet

i've been trying to find a movie a saw when i was a kid. Don't remember the name, just few details of the plot. I remember it was set on mars, there was a human colony there, like a dome city. They had a conflict with an alien race that looked like furry humanoids. The main characters wher two kids, a boy and a girl. The girl had an alien pet, a little fur-ball animal. Eventually they meet the "enemy" alien race and find out that their pet is an infant of that race. Eventually the aliens help the humans to make the planet completly habitable for humans, and in the end it is shown that the little pet has grown and is telling the story of the movie to some human kids. Any idea what i'm talking about or did i make it up in my mind?