poster child
noun/ˈpəʊstə tʃaɪld/
/ˈpəʊstər tʃaɪld/
(also poster boy, poster girl)
(especially North American English)- 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
（为慈善等目的）出现在海报上的儿童 - (often humorous) a person who is seen as representing a particular quality or activity
代表人物；典型 - He is the poster child for incompetent government.
他是无能政府的典型人物。
- He is the poster child for incompetent government.