Abu Hurairah (RA) reported that he (the Holy Prophet) said: Three (children) who die in childhood.
Explanation & Benefits
Shaykh Maulana Abdul Aziz Alvi
Hadith Commentary: Benefits and Issues: Parents have more love and affection for their small children, therefore, upon their death, the grief and sorrow is also greater. According to most scholars, this is a restrictive condition, meaning that the reward mentioned is for the death of minor children and not for the death of adult children. However, some hold the view that a small child is a burden upon the parents; if such a reward is given for their loss, then for a child who bears the burden of the parents and manages the affairs of the household, this reward is even more deserved, because the grief over their death would be even greater.
Source: Tuhfat al-Muslim: Commentary on Sahih Muslim, Page: 6700