From Wikipedia:

Mischievous young girl named Mia is read a magical copy of the fairly tail Thumbelina by her mother. Later, when her mother falls asleep, Mia shrinks and pulled inside the world of the book. A fairy godmother appears and tells her that she is in her mother's dream world and that in order to return to normal, she must find a way to take up her mother. To do this, she must travel to a far away southern land to find a magical crystal.