I was speaking as to a cause for people not considering it. In terms of effects of having kids, any measurable impact on the environment pales in comparison to the other factors. Most couples wouldn’t even need to buy different automobiles until a third child. Most couples wouldn’t even need to move to a new domicile for the first child, and then even well into having a second. The cost of raising children is a much more tangible and grasp-able effect for people to consider. That people don’t factor in the nebulous potential environmental effects of having children isn’t really surprising when you look at the direct and major factors they do consider.