A child who dies will be a bird from the birds of Jannah
the Messenger of Allah ﷺ was called for a janāzah (funeral) of a child, and I said: "Glad tidings for this child who is a bird from the birds of Jannah (Paradise) for it has committed no evil nor has he reached it (being old enough to be able to commit sins.)" He said: "Or it may be otherwise: Allah created parties specifically for Jannah while they were in their father's loins, and He created parties specifically for the Hellfire while they were yet in their father's loins."
دُعِيَ رَسُولُ اللَّهِ ﷺ إِلَى جَنَازَةِ صَبِيٍّ مِنَ الأَنْصَارِ فَقُلْتُ: يَا رَسُولَ اللَّهِ، طُوبَى لِهَذَا عُصْفُورٌ مِنْ عَصَافِيرِ الْجَنَّةِ، لَمْ يَعْمَلِ السُّوءَ وَلَمْ يُدْرِكْهُ۔ قَالَ: «أَوَغَيْرَ ذَلِكَ يَا عَائِشَةُ۔ إِنَّ اللَّهَ خَلَقَ لِلْجَنَّةِ أَهْلاً خَلَقَهُمْ لَهَا وَهُمْ فِي أَصْلاَبِ آبَائِهِمْ وَخَلَقَ لِلنَّارِ أَهْلاً خَلَقَهُمْ لَهَا وَهُمْ فِي أَصْلاَبِ آبَائِهِمْ۔»