Elizabeth is having trouble.

"How does Barney get big when he starts out so small?"

"Well, I think the kids imagine that the toy becomes big."

"But how?"

So I explained about imagination, and making a picture in her head, and pretending the picture is real. She still doesn't get it. She's been trying for a good ten minutes, and her Dorothy doll just won't appear in front of her in the full-size flesh. (I suppose that's a good thing - Judy Garland's been dead a long time.)

"Maybe the junior kindergarten lady will teach me," she said finally - and went off to play Wizard of Oz, without the witch.