Child category do not show on main menu / ribbon

Hi, i have a problem with a display of child categories on main menu / ribbon.
It shows only the part relative to a parent category. Why is that? Look here: http://www.dolcesenzazucchero.com/

P.s. Otherwise it shows either child either parent categories as separate titles on main menu and not as a drop down menu as I would like

Please, help!
Thanks