"Amongst the ruins of a bunker on a small Island, lies an ancient power. Sought by the evil Norokai, three children must stand between them and world domination."

Three children sounds very vague. Pick one – as I doubt there would be three distinct journeys – and tell us HOW they must prevent evil. “Stand between them and world domination” sounds awfully vague.

And who/what is sought by the Norokai, the children or the power?

Finally, rather than emphasizing the bunker and the small island, why not include the Inciting Incident that projects the three children into the story?