Why does Allah allow innocent children to be harmed and tested in such painful ways?

Believers must have faith that Allah Almighty is the Creator and Sustainer, and that He possesses ultimate wisdom in all His actions. He is not to be questioned about what He does, while they will be questioned. Furthermore, the calamities that befall humans are not necessarily a punishment; rather, they may be a test that elevates ranks and expiates sins. The true believer is content with Allah's decree and submits to His wisdom, knowing that Allah does nothing but good, even if humans do not comprehend His wisdom.