Why is a child punished by entering Hellfire if he was born into an unbelieving family and died as such, when this was decreed for him?

We believe in the perfection and justice of Allah, and that He, the Exalted, does not wrong people in the least, and His mercy precedes His wrath. Allah sent messengers as bearers of good tidings and warners so that people would have no argument against Him, and He bestowed upon humanity the means to distinguish between good and evil. As for someone who dies in disbelief, imitating their father, if they were unable to acquire knowledge and the call of Islam did not reach them, they will be tested on the Day of Judgment by having a messenger sent to them. Whoever obeys will enter Paradise, and whoever disobeys will enter Hellfire. However, concerning the rulings in this world, the children of disbelievers and their insane individuals are subject to the same ruling as their guardians.