Do I know you?

A teen girl walked up to the desk. "Where's my sister?"
"I don't know."
"You don't know?"
"That's right."
"But she was just here!"
The little lightbulb went off (one of the bulbs they used in those horrid Itty Bitty Book Lights, by the way, only not as powerful). I had helped a girl log into a computer to type a paper just a little while before. "Check the Children's Room," I said authoritatively, gesturing to the Children's Room mere feet away.
"Where?"
"The Children's Room," I said patiently, resisting the temptation to add, "You know, the room 15 feet thataway. The one that has one and a half foot high letters over the entrance that say "Children's Room." But I didn't. She'll be back for printing help, mark my words.