The Prophet ﷺ was asked about the children of the polytheists. He replied, "Allah knows best what they would have done."
حدثنا مسدد حدثنا أبو عوانة عن أبي بشر عن سعيد بن جبير
أن النبي ﷺ سئل عن أولاد المشركين فقال الله أعلم بما كانوا عاملين
Reported by Muslim in his chapter on divine decree, in the section on the meaning of "Every child is born upon fitrah" etc., hadith no. 2660, from the hadith of Abu Awana, and by Bukhari in the chapter on funerals, in the section on what has been said about the children of polytheists, hadith no. 1383, from the hadith of Abu Bishr, with the same wording.