If I had children I would be in mortal sin, for I have no wife. However, if you were to ask the same question to my Catholic friend Francis, he would answer "5".
How many children would I like to have, were I married? Like doesn't enter into it, as I have explained above. But I would not get married until I was stable enough in temporal matters to support a family. At the moment I can support myself quite adequately, but I would not do myself, my future wife and the Sacrament of Matrimony a disservice by presuming to be in any kind of temporal fitness to marry.