You talked about children being an asset versus not being an asset from a production viewpoint, but the real issue is from a family values viewpoint. Today's adults tend not to value the child because the child will use resources that the adult wants to use on themselves...this used to be called selfishness.
I would agree that the older children on the farm years ago would be an asset but you are discounting way to much the extra work that the younger children would have been before they became an asset...remember that there were no microwaves, dish washers, clothes washers, disposable diapers, modern furnaces (chop some more wood to keep the baby warm), etc...and a much lower percentage lived long enough to become an asset. And yet people years ago kept having children even with all the extra work...maybe they valued the family over stuff more then we are willing to give them credit for...or maybe they understood that children were a blessing and were willing to except the work that went with the blessing...
I would agree with you that we are no where near being “over populated”. Unfortunately most people do not see children as the blessing that God says they are.
God bless
Tiny children yes, they were more work however so are babies of all types on a farm. My father milked the cows on his grandfather's farm starting at age 7. From then on he worked. Most wouldn't allow one so young to do such labors today but as my Dad said he didn't do stuff like milk cows or hunt squirrels at that age because his mother was trying to teach him values she had him doing such so him and his younger brothers had enough food to eat.
But I agree with you on the family values of today.
Most would rather have the newest cars and the latest i-Gadgets than spend money on raising more children.