I dont think that larger children are really a bad thing.
Larger families typically share / hand down clothes / toys etc (I remember wearing clothes handed down from my sister, then handed down to another etc)
Larger families probably do take less long haul flights and possibly even short haul flights due to costs
On the flip to this, smaller families may have more disposable income to spend on the long haul flights and will possibly buy stuff and not have to hand it down, and throw away, thus increasing landfil.
Yes, larger families need more food but when the children grow older, there are more people contributing to the NSH and other services via tax and national insurance. If you think about the younger generation supporting their parents and grandparents with their contributions, if there are six children, their contibutions go further to their older generations.