a poster child for something
poster child for (something)
A person (usually an adult, not a child) who typifies or is the perfect example of a particular characteristic, attitude, opinion, cause, or type of person. Pete managed to disassemble their washing machine, fix the problem, and then reassemble it all by himself? Wow, he's like the poster child for DIY. Ms. Walsh built her fortune from nothing, through her own tireless work and intense ambition. She really is the poster child for the rags-to-riches American Dream.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
a poster child for somethingmainly AMERICAN
If someone is a poster child for a quality, activity, or situation, people associate them with it because they are a very good or clear example of it. Bethany McLean has become the poster child for financial journalists. Note: You can also say that someone is a poster boy for or a poster girl for something. There was a time when it seemed you were a poster girl for late motherhood. He's the poster boy for rugby worldwide. Note: A poster child is literally a young person who appears on a poster advertising something.
Collins COBUILD Idioms Dictionary, 3rd ed. © HarperCollins Publishers 2012