Kidsfighting.com
I should also think about possible chapters if it's a series, but maybe start with a standalone story. Avoid clichés as much as possible, but some tropes are okay for children's stories.
Plot structure: Introduction of the main characters and their conflict. Inciting incident where they are drawn into the fighting world. Training, facing challenges, developing skills. Climactic battle where they apply what they've learned. Resolution with a lesson learned. kidsfighting.com
Possible themes: Maybe a conflict between two groups of kids, or kids facing a common enemy. Maybe a fantasy element like magical powers, a secret society, or a quest. Or maybe it's more about overcoming challenges through sports or games. Wait, "fighting" could also refer to literal battles, maybe in a game or tournament setting. I should also think about possible chapters if