Praise be to Allah, and may peace and blessings be upon the Messenger of Allah. To proceed:
It is authentically reported in the two Sahihs, from Abu Sa'id al-Khudri, may Allah be pleased with him, that the Prophet, peace and blessings of Allah be upon him, said in the hadith concerning the people who will be cast into Hellfire on the Day of Resurrection:
“At that time, the child will turn grey-haired, every pregnant woman will deliver her burden, and you will see people as though they are drunk, although they are not drunk; but the punishment of Allah is severe.”
This is consistent with the words of Allah, the Most High:
“On the Day you see it, every nursing mother will forget the child she was nursing, every pregnant woman will deliver her burden, and you will see people as though they are drunk, although they are not drunk; but the punishment of Allah is severe.” [Al-Hajj: 2]
The scholars have differed regarding how this will happen. Some have said that these verses describe the severity of the terror and horror, by way of an illustrative description intended to emphasize the magnitude of the fear. In other words, the terror will be so intense that, if a woman were pregnant, she would deliver her burden because of the severity of the fear; and if a child were present, he would turn grey-haired from the intensity of the terror.
However, it has been established in an authentic hadith that this will occur after the resurrection. Therefore, some scholars held that the deceased will be resurrected in the state in which they died. Thus, a woman who died while pregnant will be resurrected pregnant, and then she will deliver her burden due to the severity of the terror. Likewise, one who died as a child will be resurrected as a child, and he will experience such overwhelming terror that even a child will turn grey-haired because of it.
This is one of the ways mentioned by the scholars for reconciling the relevant texts, and some of them regarded it as the stronger view. Nevertheless, it should be noted that saying that a pregnant woman will be resurrected pregnant requires specific evidence. Therefore, the issue remains a matter of scholarly disagreement.
There is no explicit and decisive text that allows us to state with certainty that every woman who died while pregnant will be resurrected pregnant, nor that every child will remain in the state of childhood until the end of the standing on the Day of Resurrection.
What is firmly established is the severity of the terror of the Day of Resurrection, and that the texts mention the pregnant woman delivering her burden, the child turning grey-haired, and the nursing mother becoming so overwhelmed that she forgets the child she was nursing.
And Allah, the Most High, knows best.