The worst thing you can do for the environment isn't flying; it is having a child. Having multiple, is, well.. X times worse.

Our population isn't declining either, as long as you watch it from Earth's PoV instead of whatever nation you're from.

I don't want to judge a specific person on having a number of children, and being the parent of one child I can't even fathom having five (!!!) but the general notions you made in conclusion to that I disagree with.