Animorphs

It's a normal day for Jake, Cassie, Rachel, Tobias, and Marco when suddenly a space ship crash lands near them. There they find a dying alien who tells them that the Earth is in great danger, that invaders known only as the Yeerks, are attacking Earth and plotting to take it over. He hands them a morphing cube with his last breath and thus gives them the power to morph into any animal that they touch. Now, the five young teens must brave incredible danger, with only their human brains and their animal forms to save the Earth from being taken over completely by the Yeerks.

Intro

We can't tell you who we are.
Or where we live. It's too risky, and
we've got to be careful. Really careful.
So we don't trust anyone. Because if
they find us ... well, we just won't let
them find us.
The things you should know is that
everyone is in really big trouble. Yeah.
Even You.