Depends on how far you have got. If you do not have his parents on the display then select him and press key P which will add their icons. Select one of them and either press key S (for a son) or D (daughter)
Click the new icons (or just select and press Enter) to open the menu and add details.
In many cases you can find things by selecting a person and a right click will show you options. I just had to do this to remember the key strokes for Son/Daughter