Is it true that all disbelievers will enter Hellfire, even if they possess good manners and do not harm anyone, and what about non-Muslim children?

All disbelievers to whom the message of the Prophet, peace and blessings be upon him, reached, and who did not embrace Islam, will be in the Hellfire, as Allah Almighty says: "Indeed, those who disbelieved among the People of the Scripture and the polytheists will be in the fire of Hell, abiding eternally therein. Those are the worst of creatures." (Quran 98:6). The criterion is their submission to Allah Almighty and His commands, not their good manners. Disbelievers behave impolitely towards Allah Almighty by disbelieving Him and claiming that He has a son, despite Allah having bestowed favors upon them and sent them messengers, thus they deserve His wrath. As for their children who died young, their ruling in this world is that of their disbelieving parents, and in the Hereafter, their matter is with Allah. They may be tested on the Day of Resurrection, and if they respond, they will enter Paradise, otherwise, they will enter the Hellfire. This is the most correct opinion.