On the Day of Resurrection, people will be raised from their graves and the children will also be raised in the state of childhood and youth in which they died, and they will intercede for their parents and admit them to Paradise by Allah’s mercy towards them:
It was narrated that Abu Hassaan said: I said to Abu Hurayrah: Two of my sons have died. Can you narrate to me any hadeeth from the Messenger of Allaah (blessings and peace of Allah be upon him) which will console us for our loss? He said: Yes: “Their little ones are the little ones (da’aamees) of Paradise. When one of them meets his father – or his parents – he takes hold of his garment – or his hand – as I am taking told of the hem of your garment, and he does not let go until Allaah admits him and his father to Paradise.”
Narrated by Muslim, 2635
Ibn al-Atheer said: Da’aamees is the plural of da’moos, which refers to a small creature that lives in ponds. Da’moos also refers to the one who wanders about, i.e., they go everywhere in Jannah, entering all places, and they will not be barred from any place, as children in this world are not barred from entering upon women and no one hides away from them. End quote. Al-Nihaayah, 2/279
This hadeeth clearly indicates that the children will remain as children at the time of resurrection, recompense and reckoning, and even the miscarried foetus into whom the soul had been breathed will remain as he was on the day he was miscarried from his mother's womb.