If you are simulating family life in The Sims 4, you will be looking to have a baby and the possible gender. Expanding the family obviously hinges on pregnancy and how it works. Once your Sims have WooHooed using the "Try for a Baby" mechanic, you can't really choose your baby's gender after pregnancy. However, there is a way to influence gender or outright use cheats if you really want to change it.

https://screenrant.com/choose-baby-gender-guide-sims-4/