It's sort of a shame that this book has fallen off the kids-lit radar, (look at how old the reviews are). It has a solid, basic sci-fi premise, it has resourceful, alert kids, and it is well-written for an early young reader. It's creepy without being truly scary. It's very satisfying for a younger reader to follow the plot and the development of the story. Vocabulary is at a good level. Siblings cooperate and problem solve. It's short enough to not overlabor the premise, but long enough to be "a real book".So, if you run across a copy of this somewhere, it would be a worthwhile addition to your kids library.