Well, to be honest, what's the summation you're looking for in asking a question that's pretty vague like that? In GTA IV all NPC are really as they were before, showing all walks of life while leaving children and animals out of the game. The big debate has been about equating the player with the protagonist as far as age, if that would correlate with any younger people as NPC, and no one directly knows, but I do know Sam Houser said to avoid controversy, there will be no CHILDREN in GTA, so you know, I reiterate what he has said, so people may take exception but he's one of the top commanders of ROCKSTAR operations, and not everything he has said has dictated a path for GTA or template, if you will, but for now, nothing REALLY suggests that's changing anytime soon, what we know will be likely present is more birds and animals like a dog clearly seen in the trailer
You also see peds or NPC (non player characters ...meaning, you don't control them) that try and populate locations as well as articulate various tasks, as simple as carrying bags or briefcases, cigarettes, or drinks, that spill, as you know, or operating equipment as we've seen in the trailer, a man pounding a FOR SALE sign in front of his house. In a few second snippet, we assume it's much more advanced AI for this to take place, but in GTA IV,or RDR, we see a task a NPC can be articulating is pre-programmed actions that simulate an ongoing task, it could be a sign resides in that yard, the ped comes to pound it in (some more, to sturdy it) and walks away eventually, but these are simple pre-programmed actions I believe. Until we know or see the game in action, it's assumed based on what's been done with GTA since San An on Renderware, to RAGE and Euphoria evolving with GTA IV Episodes, and Red Dead Redemption, which I use as an example over Max Payne 3 because of having spent hours playing those games in particular