Any Muslim who loses (to death) three children before reaching puberty will be admitted by Allah into Paradise because of his being merciful to them
Authentic hadithعن أنس رضي الله عنه قال: قال رسول الله صلى الله عليه وسلم : «ما مِنْ مُسْلِم يموت له ثلاثة لم يَبْلُغوا الحِنْثَ إلا أدْخَلَه الله الجنَّة بِفَضْل رَحْمَتِهِ إيَّاهُمْ».
Anas (may Allah be pleased with him) reported: The Messenger of Allah (may Allah's peace and blessings be upon him) said: "Any Muslim who loses (to death) three children before reaching puberty will be admitted by Allah into Paradise because of his being merciful to them."
Explanation
If a Muslim loses three small children, whether they were male or female, before they reach the age of puberty, then that will be a reason for the parent to enter Paradise.
Source · Narrated by Bukhari
From the Hadith Encyclopedia (hadeethenc.com).