I checked under custom gender (in Full Edit CAS), but both have the normal options selected. I turned it on figuring that might be the problem.) They are both Young Adults, and both have 90+ days before aging to Adult. The family has two kittens (not cats, kittens), so no pregnancies there, and no other members in their family.
I've removed all my mods, but I still see this. When I look at all the romantic options, they have Woohoo available, but not Try for Baby. I have a Sim couple that I've played for quite a long time, and they've been married almost that whole time. I know this thread is a year old, but I've just encountered this.