How can I identify a book I remember from childhood?

In an undisclosed city on the United States coast, later revealed to be in California near Santa Barbara, five 13-year-olds, Jake, Marco, Rachel, Tobias, and Cassie walk home one night from the mall through an abandoned construction site (which they are not supposed to do, as their parents seem worried about the area). There, they spot a blue light in the sky, which they discover is an alien spacecraft. The petrified children watch as the apparently damaged craft lands and out steps a strange wounded creature from another planet. This alien calls himself Elfangor, and he is an Andalite. He tells them of an alien invasion by a parasitic species known as the Yeerks. The human race is completely oblivious, and it does not have the means with which to fight off this invasion. Elfangor's people are also two years away from sending another force to Earth, and by that time, the Yeerk conquest of the planet would be complete. The youths are disbelieving. However, Elfangor tells them that he can give them powers to resist the imminent Yeerk occupation: the ability to touch an animal, and then become it -- a process known as "morphing." Incredulous, the teens argue amongst themselves but quickly decide that they have no choice but to accept. Within minutes of Elfangor's landing, Yeerk spacecraft have located the wounded alien. The sinister beings land, headed by a Yeerk general, Visser Three, who is in possession of an Andalite body. The children escape, leaving the wounded alien behind, and watch from a distance as the Visser morphs into a hideous monster and consumes Elfangor.