Animorphs wasn't THAT dark.
Oh? How many mainstream movies or TV shows have you seen that portray 13 year olds killing people?
That stuff just simply doesn't fly. If you get an Animorphs adaptation for either the big or small screens, it's going to be dumbed down and compromise. End of story.
It's an impossibility in this hippie PC environment of media regulation, and therefore it's best left to the reader's interpretation of the books, the kid visualizing the scenes as they read words off a page. You're never going to beat that with a movie anyway.
Look, the public and the action groups kicked up complaints about BATMAN PUNCHING DOGS. And you think they're going to tolerate middle-school kids turning into wolves and ripping people's jugulars out? Or aliens slicing a gorilla's stomach open so badly he has to hold his intestines in place?
No. Just no.