poster child

Từ điển Oxford Advanced Learner 8th

ˈposter child 7 [poster child] BrE NAmE (also ˈposter boy, ˈposter girl) noun (especially NAmE)
1. a child with a particular illness or other problem whose picture appears on a ↑poster advertising an organization that helps children with that illness or problem
2. (often humorous)a person who is seen as representing a particular quality or activity
•He is the poster child for incompetent government.
See also: ↑poster boy