Why did God not guide the child instead of having Al-Khidr kill him, and why is the asker deprived of money and a righteous child for fear of their corruption?

Allah is capable of granting wealth and righteous children, but He did not will to give everyone these things due to His wisdom and mercy. For some people, wealth corrupts them. And among His wisdom, exalted be He, is the disparity in provisions, so that some may serve others. The killing of the disbelieving boy by Al-Khidr was with Allah's knowledge that had he lived, he would have oppressed his parents with rebellion and disbelief. Thus, Allah did not will to guide all people. A servant should ask Allah for His bounty and seek wealth and children along with guidance. If one's situation becomes difficult, one should have a good opinion of their Lord, for trials may elevate one's status or increase one's reward. It is recommended to be patient, to have a good opinion of Allah, and to frequently seek forgiveness and send blessings upon the Prophet (peace be upon him), as these are among the causes of sustenance and relief.