Sorry here is the last bit lissa-bhw. Hope you like it.
Kate did a DNA test to find out who the father was. It was Tony's baby. She had the child, it was a girl. She and Gibbs raised her as their own though they never got married. Only Kate and Gibbs knew Tony was the father. Tony never knew he had a daughter. Kate and Gibbs had no children of their own. (Well, I doubt Gibbs is still fertile).