Making Characters Likable From a Narrative Perspective.
Up until it's Closure, Telltale had a history of making child characters that were...well...unlikable. Take Gabe Garcia for example. Despite the amount of development that his character went through in Episode 5 of ANF, Most Players still couldn't stand him after a mistake he made in Episode 4. Which begs the question; how does Marlon, a character who made far worse mistakes than Gabe, still manage to remain a more likable character in spite of that? It all comes down to the Concept of First Impressions.
First Impressions are very important when it comes to both writing fictional characters and real life scenarios. If you meet somebody in real life who makes a bad first impression, that makes it all the more difficult to get along with them going forward. Gabe did not make a good first impression in the First Episode of ANF due to his brooding, crying, etc; and because of that wound up having a very hard time getting on the player's good side through the rest of the Season. Marlon is just the opposite. He made a good first impression in the First Episode of The Final Season by helping Clem and AJ at the start. So that when the big reveal came at the end of the Episode, some players were STILL willing to forgive him for what he had done.
This is how you write likable characters. You make them as relatable and likable as possible at the start, giving them a good first impression, then focus on the more negative and quirky aspects of their character as the story progresses.