Mighty Jack and the Goblin King

the long version

"Like a bolt from the blue, Jack's little sister Maddy is gone, carried into another realm by an ogre. When Jack and Lilly follow Maddy's captor through the portal, they are ready for anything except what they find waiting for them in the floating crossroads between worlds. Even the power of their magic plants may not be enough to get them back to earth alive. Alone and injured, Jack and Lilly must each face their own monsters as well as giants who grind the bones of human children to feed their "beast" and a fearsome goblin king in the sewers down below. But when Jack finds himself in a tough spot, help comes from the most unlikely person: the goblin king!".