I’d like to know about the Mitzvah of Kibud Av V’Em for my son whose mother, my wife, passed away when he was eleven years old. How can he be Mekayem the full Mitzva witout a mother? In general, is the Mitzva for Ketanim?

A Mitzva can be cancelled in two ways I. Exemption from the Mitzva II. Not entering the Mitzva in the first place Your son is in the second category, he never had the obligation of Kibud Em, as far as he's concerned that Mitzva does not exist. That is Hashems will and your son is not in any disadvantage. Rabi Ro'i Margalit