Supplication for the advancement of reward during the funeral prayer
اللَّهمَّ اجْعَلْهُ فَرَطا ً وَذُخْرا ً لِوَالِدَيْهِ، وَشَفِيْعا ً مُجَابا، ً اللَّهمَّ ثَقِّلْ بِه ِِ مَوَازِيْنَهُمَا، وَأَعْظِمْ بِهِ~ِ أُجُوْرَهُمَا، وَأَلْحِقْهُ بِصَالِحِ المؤْمِنِيْنَ، وَاجْعَلْهُ فِي كَفَالَةِ إِبْرَاهِيْمَ، وَقِه ِِ بِرَحْمَتِكَ عَذَابَ الجَحِيْمِ
This supplication is made when the deceased is a baby/child (i.e. one not having reached the age of puberty).
After seeking forgiveness for the deceased, one can say:
‘O Allah, make him a preceding reward and a stored treasure for his parents, and an answered intercessor. O Allah, through him, make heavy their scales and magnify their reward. Unite him with the righteous believers, place him under the care of Ibraheem, and protect him by Your mercy from the torment of Hell.’