Nice job i for an animation maybe you should work on the running a bit to make it look like hes touching the ground a little bit more maybe some dirt come up when his foot hits the ground and slow it down a bit the running is a little to fast
backgrounds should be a tad more deep as in make look 3 dimensional for the characters to be in you can watch videos on 3d shapes to do that
characters i have no problems with the character animation they all look pretty good to me
I love the trailer but what you could do when making sequences of you're characters running, you could make them run at different angles. Also consider making character sheets for each character that way you won't be stuck drawing the character in a strange sort of view (EX: Willows nose while shes running.) Although the finished product (As you told me on Skype) will take a long time to finish, i really can't wait until the finished animation is finally completed well done Sarah and Thrash, well done! Hope to hear from you soon!