Well, you can't sue a volcano, and a baby exhaling does definitely not ruin the air in any significant sense. Cows do, though—we should definitely sue people raising cows for ruining it for everyone.
Yeah, babies exhaling (and all people too) are producing CO2 which is a greenhouse gas. So, yeah, it is significant enough to pay attention to. However, without killing off a bunch of people we can't eliminate this problem. So, I suppose it's easier to sue farmers and oil companies than individuals - let's all get on board! yay!