Is it permissible to buy from a discerning child, and what is the ruling on buying without speaking?

There is a consensus that it is not permissible to buy or sell a child who has not reached the age of discernment, except for a trifling matter according to some scholars, and this is what Ibn Qudamah and Al-Mardawi supported. As for the child who has not reached the age of discernment, his expression is null and void and has no legal validity in any transactions, until he reaches the age of seven. As for buying without words, which is the "Mu'atah" (transaction by giving and taking) sale, it is valid according to the majority of jurists, in contrast to what is authoritative among the Shafi'is.