I dont know if that might be the reason, but all the time I had my wife in my party, or her running around with her own party, I did not get any childs. I have 3 childs, but there I always rersted for a few days in the town where my wife was staying. Two Kids before I took her on adventures and one after when she was the governor of the first city I got.
I has worked pretty well that way, also in the other game where I had kids: I go to the city she stays in, talk to her...and then just wait in town until I get the message that she is pregnant. Both times I have done that before she was well over 30, maybe that helps too.