On the surface, the series focuses on five average human teenagers and an alien (from a race called the Andalites) who is average by his people's standards who, with the power of shapeshifting ('morphing') granted upon them by alien technology, attempt to prevent the takeover of Earth by a race of parasitic aliens called Yeerks.
To gain a new shapeshifting power, they must touch the chosen animal to absorb a length of the animal's DNA, enabling them to morph into that animal. As a whole, however, the series does not focus so much on kids who turn into animals to battle evil aliens while keeping up with their homework so much as it focuses on how their war affects and changes them.
These effects and changes are what separate this series from other children's, term used loosely, books and series. Children's is used loosely because while the series was marketed to children, the story was far more mature than an average 9-12 year old, the target demographic, could handle, a point clearly demonstrated by the majority of reviews at Amazon.
