Obviously making babies while both of you are out and about is a difficult affair - days on the road can really tire you out, and the less said about tight riding trousers the better.

HOWEVER, what if a new action become available if both husband and wife were in the same city to focus on making an heir?

That is, when they are both in the same city (not just same square, lets have some decorum), a new option comes available (just like "trade' does when two characters are adjacent or in same square), call it Progenerate.  Selecting it makes both sacrifice a turns action, but then a baby is born in 3 seasons time?  (Or if not 100%, make it radically improve the chance of a baby.)

Makes for another strategic option.  Go kill the monsters/collect the valuables OR stay at home....   (both involve experience and rewards?).