poster child
(or poster boy or poster girl)
Definition of poster child
noun
North American- a person or thing that epitomizes or represents a specified quality, cause, etc.:the antiglobalization movement’s poster child she’s the poster child for cosmetic surgery the poster child of gluten-free grains, quinoa is a wonderful light, fluffy grain the ever-grinning poster boy for the coastal good life
Origin:
1930s: from the use in print advertisements of good-looking young people and appealing children