If a fellow converted (his children remained gentiles) and prior to his conversion he had children - has he fulfilled the Mitzva of Peru U'Revu? (sources)
2I think you need to distinguish between "fulfilling the mitzvah", and subsequently being "exempt from the mitzvah". See the tshuva of Har Tzvi (OH 2:76).– CuriouserMay 15, 2012 at 17:21
This is part of a discussion on Yevamot 62a. The Shulchan Aruch rules (EH 1:7) that if he and his children converted he has fulfilled his mitzva. The Chelkat Mechokek there (sk 9) quotes the Marharil (#223) that even if his children do not convert he has fulfilled his mitzva.
And the Taz there says the opposite, that the children must convert also. May 15, 2012 at 17:38
1@Curiouser Just like the Shulchan Aruch himself, and the Rambam and others. I was just quoting one major opinion on both sides. Obviously CYLOR.– Double AA ♦May 15, 2012 at 17:40