Saddest animated film? Hmmm, tough one...
The death of Bambi's mother really got to me, pretty sad scene.
Brother Bear's ending got to me as well, when Koda and his mother told each other goodbye after Kenai turned back into a bear to take care of Koda. And of course the confession scene, the way Koda looked when Kenai told him the truth about his mother being dead, it really got to me how broken up he got and ran off, the background song also deepened the emotion there.
Mufasa's death in The Lion King was another tear jerker, I cried during that scene but my cousin came out of the theaters in tears XD
I believe that's all so far that I can remember.