Dandelion Fire by N.D. Wilson

Henry York never dreamed his time in Kansas would open a door to adventure—much less a hundred doors. But a visit to his aunt and uncle’s farm took an amazing turn when cupboard doors, hidden behind Henry’s bedroom wall, revealed themselves to be portals to other worlds.

Now, with his time at the farm drawing to a close, Henry makes a bold decision—he must go through the cupboards to find the truth about where he’s from and who his parents are.

Following that trail will take him from one world to another, and ultimately into direct conflict with the evil of Endor.