It was narrated from Anas bin Malik that the Prophet ﷺ said:
“There are no two Muslims (mother and father), three of whose children die before reaching the age of puberty, but Allah will admit them to Paradise by virtue of His mercy towards them.”

حَدَّثَنَا يُوسُفُ بْنُ حَمَّادٍ الْمَعْنِيُّ، حَدَّثَنَا عَبْدُ الْوَارِثِ بْنُ سَعِيدٍ، عَنْ عَبْدِ الْعَزِيزِ بْنِ صُهَيْبٍ، عَنْ أَنَسِ بْنِ مَالِكٍ، عَنِ النَّبِيِّ ـ ﷺ ـ قَالَ " مَا مِنْ مُسْلِمَيْنِ يُتَوَفَّى لَهُمَا ثَلاَثَةٌ مِنَ الْوَلَدِ لَمْ يَبْلُغُوا الْحِنْثَ إِلاَّ أَدْخَلَهُمُ اللَّهُ الْجَنَّةَ بِفَضْلِ رَحْمَةِ اللَّهِ إِيَّاهُمْ " .