Neteyam and the Sokka effect
Sokka is the big brother, he is responsible, intelligent and protective. And they do use him as a comedic relief for the most part, but no one can deny his other qualities. He is, the tallest and "biggest" of the others (until Zuko came) and you get used to that. You know who Sokka is.
Then you see him standing beside real adults, those that are truly responsible and in charge and you see how small he looks compared to them and you remember.
Same thing is happening with Neteyam.The big brother, the mighty warrior, the one who was supposed to lead after his father. The tallest of the other kids, the most responsible and most protective. You get used to it.
Then you see him next to his parents and you remember that he is just a kid. A fifteen year old that just wants to make his parents proud and be good. He wants to keep his family safe no matter what, so he follows the rules, do anything that is asked of him and more. But when you really look at him you remember that he is not yet a mighty warrior but a child trying to be good.