From my experience, in order to make them fall in love and have a romantic relationship with one another, you choose the romantic interaction category and have one sim "confess feelings" for the other sim, changing their relationship status to romantic interest. After this, have your sims interact with one another romantically until the option "propose going steady" appears. This changes the romantic status to boyfriend/girlfriend. Continue to have your sims interact romantically with one another until "propose marriage" appears (the sim that proposes will keep their last name and change the other sim's last name to theirs) their relationship status will change to fiancé and fiancée. After this, there will be an interaction option to get married; there are two different options, you can have a public wedding (where your sim uses their phone to plan a party, there will be an option for wedding, choose that, then when the party has started, choose the interaction to "exchange rings", all nearby sims will gather around and the two sims will get married) or a "have private wedding" (you can choose the interaction have "private wedding" at anytime when there isn't a party.) Both options change relationship status to husband and wife.
When your sims are ready to start a family, have your sims interact with one another romantically until "Woohoo" and "Try for Baby" options appear, that or have one sim relax on a two-person bed and interact with other sim which will include option "Woohoo" and "Try for Baby." With both the interactions, "Woohoo" and "Try for Baby" there is chance that the female sim can get pregnant, but "Woohoo" has a very small chance but "Try for Baby" has a very high chance, if a lullaby plays at the end of either of these interactions the woman is pregnant. These options are available at any stage in the relationship, so they don't have to be married for the woman to get pregnant. If the woman is pregnant she will begin experiencing morning sickness around the next day (frequent nausea moodlet and vomiting from unknown causes.) About a day later, the woman will begin to show; pregnancy lasts three days (four if you count morning sickness) and each day will get bigger, at about the end of the third day, she'll start to go into labor; she can either give birth at home or go to hospital and give birth there. Then there will be a notification that a healthy baby boy or girl is born (or if your lucky twins or triplets) and you will be able to name the newborn and most likely choose his or her first two traits. You actually have control of the baby's sex/gender: if you want a boy, have the pregnant woman eat apples, and if you want a girl, have her eat watermelons, three of the desired fruit gives you about a 99.9% that the baby will be the desired sex.
There's also the possibility of adoption, have one the sims use their phone and for services, click on that and choose the adoption agency option. You will be able to choose if you want a boy or girl and if you want an infant, toddler or child. The adoption agency will notify you that your baby/child will be delivered shortly and when they arrive then you can choose their name. They also already have traits given to them. This is a good option if you have a same-sex/elderly couple, you can't seem to get your female pregnant, your single wants a child and/or you don't want to start with a newborn.
I know this is a lot of information but I thought it was important and being an experienced sim player, I thought I'd share it with a new player asking for help. I hope this help and will work for you. Happy Simming! 😕mileyhappy:
