Abu Sa‘īd al-Khudri (may Allah be pleased with him) reported that the Messenger of Allah (may Allah's peace and blessings be upon him) said: "Al-Hasan and Al-Husayn are the chiefs of the youth of Paradise."
عن أبي سعيد الخدري -رضي الله عنه- قال: قال رسول الله -صلى الله عليه وسلم-: «الحَسَن والحُسَيْن سَيِّدا شَباب أهْل الجنة».
شرح الحديث :
Al-Hasan and Al-Husayn, sons of the Prophet's daughter Fātimah are the cream of the youths of Paradise. In other words, they are the chiefs of the youths of Paradise, except the prophets and the rightly guided caliphs. In Paradise, people will be of the same age; the youth age. The Hadīth could probably mean that they are the masters of all those who died young and entered Paradise.