Show me.the scripture that says they did. Oh Brother Don, come now. We're not having Dan Brown write our theology are we?Provide the verse that says neither married and that neither had children.
Paul said himself he was single and wished all to remain so. The whole Jesus having children thing has been done to death and we won't solve it here but you can at least admit that scripture doesn't record that He had children and in fact makes it highly unlikely.
A better answer would be to say that we can multiply through children or we can multiply through evangelism. You don't need to invent families for Christ and Paul, the two most confirmed bachelors in Christendom. And you can't read the New Testament and think that celibacy is a sin.