I don't know as the 'happy kid story' is not fully described. But it probably has the kid as the main character.
In the 'happy kid story', there could be the happy kid of course. There might also be the kid's parents, siblings or friends. If it's a school - related story, there could be teachers or classmates. And if it's an adventure - type story, there might be some interesting strangers the kid meets along the way.
Since we have no details about the 'happy kid story', the characters could vary widely. It could be a story where the main character is a lonely kid, and then new characters like a friendly neighbor or a kind - hearted coach enter the story and change the kid's life for the better. There could also be some animals in the story if it's a more imaginative tale, like a pet dog or a magical unicorn that the kid befriends.