What did Sheikh al-Islam mean by his statement that the Islam of a child does not take him out of disbelief, and is this correct?

In his book, "Minhaj as-Sunnah an-Nabawiyyah," Sheikh al-Islam Ibn Taymiyyah responds to Ibn al-Mutahhar al-Hilli, who denied the Imamate of those who preceded Ali, citing the verse: "My covenant does not extend to the wrongdoers" [Quran 2:124], and claiming that the three caliphs were disbelievers who worshipped idols. Ibn Taymiyyah countered this argument by stating that the entire Quraysh tribe, including Ali, worshipped idols before the prophetic mission. He further explained that the disbelief of a child is not like the disbelief of an adult, just as the faith of a child differs. He pointed out that the Islam of the three caliphs (Abu Bakr, Umar, and Uthman) undeniably removed them from disbelief, by the consensus of Muslims, whereas there is a disagreement regarding the Islam of a child, such as Ali. Imam Shafi'i, for instance, held the view that the Islam of a child does not remove them from disbelief.