Read a book about an inventor or scientist. Try doing some of their experiments or using some of their inventions. Try creating your own experiments or making your own inventions. Be sure to decide in advance what age you are writing for. Try creating quizzes or games based on popular books.
Games are really hard.
We did this a few years ago. It's hard to make a game that is not boring and that lasts the right amount of time. We had to keep playing the games and making changes. We also found it hard to write clear directions. It's extremely educational, though, and interesting.