From the Mixed-Up Files of Mrs. Basil E Frankweiler (Yearling Newbery) - Softcover

Two runaway children make their home in the Metropolitan Museum of Art

decided to run away, she planned very carefully She would be gone just long enough to teach her parents a lesson in Claudia appreciation.  And she would live in comfort-at the Metropolitan Museum of Art.  She invited her brother Jamie to go, too, mostly because he was a miser and would have money
The two took up residence in the museum right on schedule.  But once the fun of settling in was over, Claudia had two unexpected problems: She felt just the same, and she wanted to feel different; and she found a statue at the museum so beautiful she could not go home until she had discovered its maker, a question that baffled even the experts.  The former owner of the statue was Mrs. Basil E. Frankweiler And without her help Claudia might never have found a way to go home.