Try for baby paralives - how?

It's under the romantic interactions, not the friendly ones. Get the two of them to a proper couple relationship first, then with one of them selected click the other while you're near a bed and the try for baby option should be in the romance list. If you're only seeing the regular couple stuff with no baby option, the relationship probably isn't far enough along yet, or one of them isn't an adult. That's what tripped me up on my first save.