gigantic [Rosie] I direct your attention to the end of this page where they point out that certain Anglican clergy who have married, and later converted to Catholicism, have been permitted to remain married after becoming Catholic priests. If such a priest ascended to the papacy, he could have daughters.
fur [Rosie] Another possibility relates to papal infallibility. The Pope could easily make a pronouncement through extraordinary Magisterium to the effect that the rule about celibacy in the priesthood does not apply to the Pontiff himself. Even if this contradicted previous teaching, such pronouncements are by definition never theologically or morally incorrect. He would then be free to father as many children as he wanted, at the risk of causing a schism in the church!