Before I leave VF for the night or just to go away from it for several hours, I try to get a new baby conceived in each of my families that are "eligible" (not too soon after a previous one, not too old or full house). That way, when I come back to the game, the nursing period is over and the infant has transitioned to a child.

Incidentally, if you try and it is "too soon", just wait about 15 mins and try again.