The only game referenced that I've played is Bastion, which isn't bleak at all, and Limbo, which was an enjoyable diversion. I was never under the impression it was attempting to be 'artsy.' It had a unique art style to be sure, and the art style played a direct role in setting the tone and setting; however, the art was not the main attraction, nor did I detect the familiar of odor of pompous self righteous superiority that typically accompanies hipsters attempting to deconstruct a visual theme. In light of this, I am wondering what Yahtzee means by 'artsy.'
I think the rash of kid-centric games is the result of the age of the game developers making those games. As a thirty-something year old myself, it wasn't until recently I transitioned from 'kids are disgusting, expensive little shit bags' to 'some of them are cute, I might want one.' In fact, my unpublished literature has explored this transition in my life, and I've found myself attracted to media exploring parental relationships with children, such as The Last of Us and The Walking Dead. I found myself even forcing this relationship into Dragon's Dogma, a game not originally intended to be played that way, by making a father/daughter character and main pawn combination.
In summary, I'm not sure the kid in a scary world trope is utilized to be artsy. I think it's just a product of maturing game developers, and their maturing customers.