I think that is a valid question about the boys and the girls. I am not quite sure. Bruce Hozeski actually wrote a whole article that essentially breaks down the math of Swift's proposal and finds that if the people of Ireland had taken him seriously, the whole population of poor Irish people would be wiped out in a short manner of time. His estimations were far from perfect and I think were meant more to make an example of things rather than really set an expectation. I did a bit of extra research and did not find any plays that have been modeled after A Modest Proposal.