putty in someone's hands - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
A person who is easily influenced or malleable, as in Dean adored his little granddaughter; he was putty in her hands. This metaphoric term, first recorded in 1924, transfers the malleable quality of putty to human behavior. Also see twist around one's finger.