A young child that R”L loses a parent when does he say kaddish for the parent? When he is still a child or only when he becomes Bar Mitzvah and then says for 11 months? Is there any difference in this with the Ashkanazim and Sephardim?
A child who is able to should say kaddish when his parent dies, and not when he reaches bar mitzvah.
The Gesher Hachayim (vol. 1, p. 325) writes that although some poskim write negatively concerning children saying kaddish, this refers only to an obligatory kaddish as part of the prayer service, and not to the mourners’ kaddish.
See also: Shut Devar Shmuel 301; Levush 133:2; Beis Yehudah Orach Chaim 22. In fact, the Rema (Yoreh De’ah 376:4) writes that the entire mourner’s kaddish was enacted for children to recite!