Family C is a mod by Jin Ryuu that lets you make and mange a family. It also lets you use a female model and spawn children. though the last one is probably still in development.
You can use the interact key to interact with the mod. Default the Key is B but it can be changed in options.
Pressing it while not looking at another player will open up the Family C GUI, showing details about you and your family, and letting you manage some things, like starting a family.
if you press interact on another player it will show you their stats and you can ask them to join your family or if you can join theirs, either as a spouse or child.
Through interacting, this mod lets you start and manage a family. Setting other players a spouses kids and parents. past making those connection though, the family mechanic doesn't seem to have much impact on game play just yet.
When you make edit your avatar in the Character creation menu, with this mod and JBR installed you're characters shape will actually change.
You can use a command to spawn children. their seems to be no other way to do this so best guess is this is an experimental function for right now.