Meaning: This sentence uses figurative language to describe the power of the crayons in the children's hands, as if they were magical tools that can create anything they imagine.
Choice of Words: Crayons are sticks of colored wax used for drawing or writing. Become means to change or transform into something else. Magic wands are mythical objects that can grant wishes or perform magical feats. In their hands refers to the children holding the crayons.