The Letter F is for Fun
If the story is fiction and on a serious topic, you may have more success if you add age appropriate humor somewhere in the story to make it more realistic. Life is serious too but there are periods of time where a little fun can make the moment more meaningful.
If you write for children make certain that you also keep the fun in your writing time. If you don't enjoy the process and are not having fun, it will show in your work.
Use these fun F words to write a 200-400 word story for sixth grade readers. And have some fun with this mini-project.
fathom, ferry, feud, fidelity, flair, fleece, flirt, fluorescent.