Invocations for a child in the Funeral prayer
 

أللَّهُمَّ أَعِذْهُ مِنْ عَذابِ الْقَبْرِ

160. Allaahumma 'a'ith-hu min 'athaabil-qabri

O Allah, protect him from the torment of the grave. 

or say: / tabi wipe: 

اللهُـمِّ اجْعَلْـهُ فَرَطـاً وَذُخْـراً لِوالِـدَيهِ، وَشَفـيعاً مُجَـاباً، اللهُـمِّ ثَـقِّلْ بِهِ مَوازيـنَهُما، وَأَعْـظِمْ بِهِ أُجُـورَهُـما، وَأَلْـحِقْـهُ بِِصَالِـحِ الـمؤْمِنـين، وَاجْعَلْـهُ في كَِفـَالَةِ إِبْـراهـيم، وَقِهِ بِرَحْمَـتِكَ عَذابَ الْجَـحِيمِ , وَأَبْـدِلْهُ داراً خَـيْراً مِنْ دارِه ، وَأَهْلاً خَـيْراً مِنْ أَهْلِـه, اللَّهُمَّ اغْفِرْ لإِسْلافِنَا , وَأَفْراطِنَا , وَمَنْ سَبَقَنَاَ بِالإِيمَان

Allaahum-maj'alhufaratan wa thukhran liwaalidayhi, wa shafee'an mujaaban. Allaahumma thaqqil bihi mawaazeenahumaa wa 'a'dhim bihi 'ujoorahumaa, wa 'alhiqhu bisaalihil-mu'mineena, waj'alhu fee kafaalati 'Ibraaheema, wa qihi birahmatika 'athaabal-jaheemi, wa 'abdilhu daaran khayran min daarihi, wa 'ahlan khayran min 'ahlihi, Allaahum-maghfir li'aslaafinaa, wa 'afraatinaa wa man sabaqanaa bil'eemaan.

O Allah, make him a precursor, a forerunner and a treasure for his parents and an answered intercessor. O Allah, make him weigh heavily in their scales (of good) and magnify their reward. Make him join the righteous of the believers. Place him in the care of Ibrahim. Save him by Your mercy from the torment of Hell. Give him a home better than his home and a family better than his family. O Allah, forgive those who have gone (i.e. passed away) before us, our children lost (by death), and those who have preceded us in Faith.

Reference: Ibn Qudamah, Al-Mughni 3/416 and Ad-Duroosul-Muhimmah li-Aammatil-'Ummah, pg. 15, by Shaikh 'Abdul-'Aziz bin Baz.

اللهُـمِّ اجْعَلْـهُ لَنا فَرَطـاً، وَسَلَـفاً وَأَجْـراً

161. Allaahum-maj'alhu lanaa faratan, wa salafan, wa 'ajran.

O Allah, make him for us a precursor, a forerunner and a cause of reward.

Reference: Al-Hasan (Al-Basri) used to recite Burnt Al-Fatihah for a child's funeral and then say. Al-Bukhari, Kitabul-Jana'iz, p. 65.