From here:

Your net carbon impact depends far more on the number of children you will have than any other variable; remember good environmentalism uses a zero rate of discount. So people with no biological children should be allowed to fly a lot and people with lots of biological children should not get to fly so much at all. Is that so far from the reality we observe?

Seems like the incentives are aligned all around on this. It's rough flying with kids, both on the parents and all the other fliers who empathize but really wish their noise-canceling headphones could filter out the high-frequency screaming of a distressed child.