One of the things I just happen to try is when they're in the bedroom trying to make a baby and once they start kissing, I would click over and over on the mom, and at least four times the baby appeared and they did have the baby (this doesn't happen all the time. You might want to try this. Just thought I'd share this tip that has worked for me. Hope this may help if anyone has this same problem.

In one of my games I was on my 22 generation and they wouldn't have any children, even though it said they wanted children. My game started over all over again as a new game. Lost all the upgrades, improvements and collections. I did write into the forum and got a answer on maybe how to get the game back.