The Way to Rio Luna by Zoraida Córdova

From Scholastic: 

Eleven-year-old Danny Monteverde believes in magic. He knows that pixie dust is real, that wardrobes act as portals, and that rabbit holes lead to Wonderland. Most of all, he believes that his older sister, Pili, is waiting for him somewhere in Rio Luna, the enchanted land in their favorite book of fairy tales.

Danny doesn't care what the adults say. He knows that Pili isn't another teen runaway. When the siblings were placed in separate foster homes, she promised that she'd come back for him, and they'd build a new life together in Rio Luna.

Yet as the years pass, Danny's faith begins to dim. But just when he thinks it might be time to put...