Will children who die a few months after birth intercede for their parents if no aqiqah was performed for them, and is it obligatory to perform the aqiqah for them after death?

What was mentioned in the question, quoting Imam Ahmad ibn Hanbal when explaining the hadith: "Every child is mortgaged by his aqiqah," is that its meaning is "detained from interceding for his parents." "Mortgage" (rahn) in the Arabic language means "detention" (habs), and he is prevented or detained from a good that is intended for him. The aqiqah is necessary and indispensable, so its necessity and the inability of the newborn to be detached from it were likened to a mortgage. Al-Hafiz Ibn Hajar narrated from Al-Khattabi that the best opinion on this matter is what Ahmad ibn Hanbal held regarding intercession. The aqiqah is an emphasized Sunnah according to the majority of scholars, and it was said to be obligatory in one narration from Imam Ahmad. Therefore, it is desirable for the father to perform the aqiqah for his children if he is able.