Adds children to the game. Their stats are tweaked slightly compared to adults and have unique restrictions/interactions that make the base game admittedly a little more interesting. The most annoying feature is that these children have voice lines that play nonstop while you're managing your base and because they run around a lot, you'll hear a LOT of heavy breathing like they're right up against your ears.
Nothing groundbreaking in terms of changes to overall gameplay; I'd rather suggest choosing one of the Stories DLC's for more content and a better This War of Mine experience.