ToonDoo: OK, so it is homework, but at least it's fun!
Below, some of the links I provided in a creative writing workshop I gave recently for Macmillan (and welcome to any of you who came/are coming in Girona, Lleida or Palma!).
Cartoons and animations
Note that Dfilm MovieMaker is possibly not suitable for young learners.
Personally, I have a preference for using good old Word, or even PowerPoint, or (best) a blog, for creative writing as I think that with some of the above your learners will end up spending more time on the technology and less time on the writing and the interaction in English (with the latter being what we're really trying to obtain in the language classroom)…
But I accept that, especially with younger learners, being able to animate things is probably more exciting, and hence more motivating and engaging and thus as likely as anything to produce learning.