Sayyidah Umm Sulaym bint Milhan (may Allah be pleased with her), the mother of Sayyiduna Anas bin Malik (may Allah be pleased with him), narrates that the Prophet (peace and blessings be upon him) said: "Any (husband and wife) whose three children die before reaching puberty, Allah Almighty will admit them both (husband and wife) into Paradise by the grace of His mercy." He said this three times. I said: "O Messenger of Allah! And if there are two?" He said: "And if there are two (the same reward will be attained)."
Imam Ahmad and Imam al-Tabarani in al-Mu'jam al-Kabir recorded it. Its chain contains a narrator, Amr bin Asim al-Ansari; I have not seen anyone declare him trustworthy or criticise him, and its remaining narrators are the narrators of the Sahih.
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب الجنائز / 3985