How do I add a child or children born out of wedlock, but with a known parent?

Perhaps this may help:

One of the most direct ways to add a child into Family Tree is to link them to their parents.

If one of the parents of the child is unknown, click Add Child with an Unknown Mother or Father. Add details in a note or in the individual's Life Sketch.

Please click on link for more information How do I add a child to Family Tree?