Can't try for baby or woohoo

Okay, here is my problem. I have two sims who are married to each other with full romance and friendship bars (yes, I used cheats to get them that way) but whenever I tell them to try for baby or anything else to do with each other they just stand there and do not do anything. The try for baby command is in their queue, but it wont do anything. They each have been doing nothing but standing there for 10 sim hours now, and if I tell them to do something else the try for baby command disappears. Help?