No two Muslims lose three children who have not reached puberty but Allah admits them both into Paradise by His mercy

It is narrated from al-Harith bin Uqaysh (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Any two Muslims whose three children die before reaching the age of puberty, Allah Almighty will admit them both (the parents) into Paradise by the grace of His mercy to them." The people said: O Messenger of Allah! And one whose two children have died? He (peace and blessings be upon him) said: "And one whose two children (have died, him too)." And the Messenger of Allah (peace and blessings be upon him) further said: "Indeed, among my Ummah are people through whose intercession more people will enter Paradise than the entire number of (the tribe of) Mudar, and among my Ummah there will be (a sinner) who will be made so huge for Hell that he will become one of its corners."
The chain of this hadith is sahih (authentic) on the condition of Muslim. Al-Harith bin Uqaysh is mentioned in the Musnad collections of the imams, and this is of the type we mentioned earlier, where a single Tabi'i is alone in narrating from a Companion (which is a defect in the view of the two Shaykhs).

It is narrated from al-Harith bin Uqaysh (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "A man of my Ummah will (be one who will) enter Paradise and then intercede for more people than the entire number of (the tribe of) Mudar."