poster child

From the usage of appealing young people and children in charitable advertisements.

• "He's a poster child for militant vegetarianism."
• "I think he smile could have opened the door by itself. It seemed to have a life of it’s^([sic]) own with snow-white teeth below sparkling blue eyes. Its owner could be the poster child for the expression “grinning from ear to ear.”"
• "“He’s not exactly a poster child for the average well-adjusted American kid. He’s only been in-country for a few days.”"
• "A visit to Adventure Island–an after-school program developed by Robert Slavin and Nancy Madden, professors at Johns Hospkins University and creators of Success for All, a comprehensive school reform program practiced in hundreds of schools across the country–could be the poster child for what some might call the academic approach."
• "But it isn’t difficult to see why Lawrence, who has since become the poster child for healthy body image, elicits such strong reactions — particularly in GIF form, where differences between the original and Photoshopped images are clear."