First, to start, add your former spouse (s).
For this, click on your button and click "Add a wife / husband" (1).
Like when you add in the near your tree, a new window will appear where you can complete its information.
Once the profile is created, click again on your box and choose "Add a son" or "Add a daughter." (1)
A new window will appear in which you have to choose the other parent of your child.
Once selected, fill your child's information and confirm.
His profile will then be added to your tree and will be attached to your box and that of your former spouse (s).