I read a sentence in "The Hindu" which was:
Like all playgrounds, even YouTube has its popular kids on the block.
According to most of the dictionaries, "on the block" means "up for auction". Does that make sense here?
The word "block" has many definitions, but in this case a "block" is the area between two parallel streets. So there are many common phrases like "popular kids on the block", "new kids on the block", where "on the block" means something like "local" or "neighborhood" (adj.). The phrase "popular kids on the block" is like saying "the local popular kids" or "popular kids who lived on that street", "popular kids in that neighborhood.".
In this specific context, it is just saying that there are certain personalities who are popular on Youtube, and conveys a certain sense of these "popular kids" having a lot of social capital and maybe being a bit cliquish or exclusive.