The Sims Mobile only let you create a mature sim. In this game, there are only adults: no children, no elderly.
At some point, you will be informed that your sim can get a retirement now. If you agree, you will loose the sim, who will move out, leaving an heirloom. The decision is up to you, though. If you want to do that, you need to open the sim's attributes - that's where the retirement info will be waiting.
In order to have kids, you need to have a love relationship at level 8 and at least 11th experience level. Then you only have to buy a cradle and click it. There will be a few options to choose from. You will be able to either adopt a kid or have your own. The baby will instantly appear in the cradle.
You cannot control the baby. You can only control it when it becomes an adult. The sim doesn't have to take care of the baby - you can have an event with him or her once a day. This gives them character points. The kid grows up independently.
You can have a kid with both men and women - the only requirement is level 8.