a child with a particular illness or physical problem who is used in a poster advertising the work of an organization that helps children with that illness or problem （出现在宣传海报中的，患某种疾病或面临某种问题的）海报儿童
2
humorous someone whose behaviour or character represents a particular quality （行为或性格的）代表人物，典型人物
William is a poster child for incompetence. 威廉是典型的窝囊废。