The Giants and the Joneses - Julia Donaldson

Jumbeelia the young giantess loves to hear the old story about the iggly plop who climbed up the bimplestonk to the giants' land of Groil. Then, one day, she throws a bimple over the edge of Groil.
Down, down, down Jumbeelia climbs--right down into the land of the iggly plops, where she discovers Colette, Poppy, and Stephen Jones; puts them into her canvas bag; and carries them back to Groil.
Soon the children find themselves shut in her dollhouse, with no visible means of escape. With danger surrounding them at every turn, the children must use all their wits to survive and figure out a way to get back home. . . .