Poster child/boy/girl American British noun phrase
A child, boy or girl, who exemplifies or is the ideal representation of a specific quality
James got by to fix the leak of the water pupe and amended the roof all by himself. Wow, he's actually a poster boy!
After leaving the school, she immediately goes to her charity club, allocates the food, and delivers them to the poor. She is a poster girl for volunteering.
He managed to balance the study and work for over 4 years, He was the poster boy for overcoming difficulties in life.