The ruling on whomever died from the Children of the Polytheists

Question :

The child who was born of two disbelieving parents and died before reaching the age of puberty, is he considered by Allâh to be a Muslim or not? This is while knowing that the Messenger of Allah said:
"Every child that is born, is born upon Al-Fitrah (i.c., Islam)."

And if he is a Muslim, is it obligatory upon the Muslims to wash his body and pray over him? Please benefit us with an answer, and may Allâh reward you.

Answer:

If someone who has not reached the age of puberty and who has two disbelieving parents dies, then his ruling is the same as that of his parents concerning the rulings of this life. Thus, he is not to be washed or prayed over or buried in the graveyards of the Muslims. However, in the Hereafter, his matter is left to Allâh. Indeed it has been authenticated from the Messenger of Allâh that when he was asked about the children of the polytheists, he said:
"Allah knows best what they were doing."

Some of the people of knowledge held the view that Allâh's Knowledge concerning them will be manifest on the Day of Resurrection and that they will be tested just as the people who lived during a time that no Prophet was sent, and others similar to them, will be tested. If they respond positively to what is requested of them, they will enter Paradise; and if they disobey, they will enter the Fire. Hadiths have been authenticated from the Prophet regarding the testing of the people of Al-Fatrah on the Day of Resurrection. They are those whom the propagation of the Messengers did not reach, and whoever has their ruling, like the children of the polytheists. This is due to the Statement of Allah:
"And We would not punish until We have sent a Messenger (to give warning)."

This statement is the most correct of the statements concerning the people of Al-Fatrah and those similar to them, whom the Divine message did not reach. This is also the view chosen by Shaykhul-Islam Ibn Taimiyyah and his student, the great scholar Ibn Al-Qayyim, as well as a group of the Salaf and the Khalaf (those who came later). May Allâh have mercy upon all of them. And Allâh is the Giver of success.

Source:
Ash-Shaykh Ibn Baz
Fatawa Islamiyah, Vol. 3 Pages 146-147-148