Story Board That:
https://www.storyboardthat.com/storyboard-creator
This is a handy and fairly intuitive website that allows the user to create a story or comic using a a variety of characters, images, scenes, and uploaded images. It appears to work on the iPad as well.
Here is a sample illustrating student's need for movement and heavy work:
Also see:
10 Sites / Apps for Creative Writing
http://www.slideshare.net/rbyrnetech/10-sites-apps-to-inspire-creative-writing
https://tp053.k12.sd.us/Following%20Rules%20at%20School.htm