If I remember correctly "Learning to Love" has Mayson come close to breaking up Clark and Lois's marriage, but if there is a child there at the start of the marriage it isn't Clark's.
Carol M has another one where Lois and Clark get into a shotgun wedding in Latislan. I don't remember when Clark gets around to telling Lois that he is special in that one. It might not be until after she has their second child, so it might not be until after the kids are born.
