The Meaning Of "Every Child Is Born In A State Of Fitrah" And The Ruling On The Dead Children Of The Disbelievers And Of The Muslims. Sahih Muslim 2660
Translation
Abu Huraira reported that Allahs Messenger (way peace be upon him) was asked about the children of the polytheists who die young. Thereupon Allah's Apostle (ﷺ) said
It is Allah Who knows what they would be doing.