Yeah, I kind of think this too.
In fact, one of the things about the environmental impact of children is that it's often the kids in western countries, not in places where they have larger families, that have the largest footprint. Why? Because the parents try and give those kids a luxurious (in worldwide/historical terms) lifestyle. Those kids grow into adults that see that as "normal" and expect a similar or better lifestyle as adults and for their kids.
In bigger families you typically see kids sharing rooms, with hand me downs, having to decide of which activities to pursue or choosing less expensive ones, entertaining themselves, taking far fewer trips to less exotic locales. They don't grow up into adults who believe they need two or three bathrooms, an overseas holiday once a year, etc. This is a good thing.