Yosef Karo, Shulchan Aruch — Yoreh Deah 392
“ And if he has not yet fulfilled the command to be fruitful and multiply or if he has small children or that he does not have someone to serve him, he is allowed to betroth immediately and to marry after the Shiva; and he should not have relations with her until after the thirty days except that if he has yet to fulfill the commandment to be fruitful and multiply he can have relations with her after Shiva. ”
