Educating children: any tricks? I chose genius people with great traits but my kids turn out shit!

Found a 15+ courtier of the same culture, genius and all the nice things...

Oh sorry, your son is now a greedy craven hunchback...

This seems to be the story of my rulers life. Fortunately I have feudal elective and can avoid them... but the next son seems to turn out just as bad.

There has to be some tricks I just don't understand. Any advice?