Kaddish

At Ma’ariv, a boy under bar mitzvah recited Kaddish Yatom. When he finished, people told him to say Barchu as well. Was that proper? If not, should I have answered?

n my shul, at the end of An’im Zemirot, the chazan (child) does not say “Lecha Hashem hagedula …” I understand that it is not permitted to say Kaddish after a shir (song of praise) without p’sukim. Can you provide me with sources to prove this?

I am in the midst of the year of Kaddish/chazanut for a parent. Two brothers have been davening due to shloshim. After they finish shloshim, should we have a rotation of three or, considering that our recitations are to bring merit for the deceased, should I be chazan half the time? (We will not fight over it but would like to do the correct thing.)