to get your Sim pregnant you need to make them both like each other then you get them to both relax in a double bed at the same time them click on they other one and then click try for a baby
You cant, however you can on Sims Castaway life stories, when 2 sims of opposite gender are lying in bed, (given your reputation is high enough) select "Make a baby".
I realy dnoHannahluvsthesims2: If you have the sims origional, you can either kiss a whole bunch, or buy a bed that ahs a heart. Then relax both sims on it (boy and girl) and click Woo-hoo sometimes...
You may have both Gender Sims in a bed, and relax them on the bed, click on one of the sims, and it will say try for a baby. After they are done and asleep tere might be a soft tune. If there is that...