May the mother of the baby boy attend the seudah of the bris l’chatchila if she is still in the year of mourning for a parent. Also may the mother of the bar mitzvah boy attend the seudah of the bar mitzvah if she is still in the year of aveilus for a parent?
The mother of the baby may attend the bris and the meal during the year of aveilus, even if there is music there. This is because it is considered her simcha, that she was zoche to bring child into the covenant with Hashem. Also the mother of the bar mitzva boy may attend the seuda.
Hamakom yinachem eschem b’toch shar aveilie tzion v’yerushalayim,
Chazal say that when a boy is born it is a consolation for the whole family.
Mazal Tov, and enjoy
Chida in Chaim Sha’al 21, Divrei Sofrim Aveilus 391- 30. Regarding Bar Mitzvah see Shut Zera Emes 3- 168, Divrei Sofrim ibid.