@Bobby68 "having more children means, they are not of age to work yet, so this doesn't impact...as of yet...how many workers Ireland has"

This is true.

Although (A) is a very bad explanation, the main reason I chose (D) over it was picturing a bunch of toddlers running the farms.

I just treated the unless as a rule instead of another sufficient condition.

Still arrived at the right answer, but probably still need to understand embedded conditionals better.