Here are some possible ideas for your animations. Good luck!
Predator and prey – Choose an animal that will chase another animal.
Dinosaurs – Two dinosaurs can chase each other or have a fight.
Aliens – Aliens can zoom around space or land on a new planet.
Fairy tales – A prince or princess can go on a short adventure.
Mini-beasts – Insects could crawl across the page and scare somebody.
Transport – Cars or planes or boats could race around the screen.