Children are not supposed to rescue their parents, life is supposed to be the other way around. And rescues aren't supposed to be needed on the trip out to the new colony planet Valhalla. Slow, yes. Boring, yes. Dangerous? No, the trip is not supposed to be dangerous, never has been.
When thieves attack the transport ship to steal an ancient alien artifact, and young Kaylee and her brother, Manny, are cut off from their parents, they have to stop the thieves from getting what they want, because once the thieves have the artifact, they're not leaving any witnesses.