Sick children take upon themselves the exploit of martyrdom and foolishness in order that the Lord would not vent His wrath upon this world, and that we, perhaps thanks to them, mightstill have time for repentance. Yes, God is just. He does not teach us to sin. We wouldn't have any problem with the question of why it is children suffer if in this matter, as in everything, we looked upon Christ the Saviour and measured our life in light of Him. After all, He was sinless.
Every child is born into the world bearing upon itself the stamp of ancestral sin.
But the Lord didn't even have this. Here, then, is the answer to the question of why children suffer. For our sins. For our carelessness concerning the salvation of their souls and our own salvation. Our task as parents consists not only in providing for our children's physical needs but primarily in educating them spiritually, in opening up for them the path to God.