Because preschool children are in the stage of figurative thinking, children at this stage can quickly remember Chinese characters like pictures through image memory. Just like the evolution of the word "water"
The function of Pinyin is to "read", not "recognize". "Literacy" is the core of children's literacy, which is to let children understand the meaning of a word and then know the sound.
So the function of Pinyin is to let children learn the pronunciation of Chinese characters in Putonghua and learn the pronunciation of a word.
Moreover, if a child can read and learn Pinyin again, he will only be unfamiliar with Pinyin, and there will be no "abstract Pinyin" and "unfamiliar Pinyin Chinese characters", which is naturally easier to learn.