What is Divine Justice in the suffering of childhood, and is one rewarded for this suffering?

The questioner is given good tidings: Indeed, Allah Almighty does not waste the reward for the suffering of children from illnesses; rather, He compensates them with something better. Al-Qurtubi mentioned that Allah has bought from children just as He has bought from adults, afflicting them with pain and sickness, then compensating them.

The reward of those children who are afflicted with tribulation is not equal to that of those who are spared from it. Children vary in their rewards and recompense according to their state and deeds. A child is rewarded for his illness and recompensed for his good deeds, but not for his bad deeds.