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