Is it obligatory to teach children matters of their religion and worldly affairs from the age of seven, and is "Play with him for seven, teach him for seven, and accompany him for seven" a hadith or a saying, and is a child exempt from accountability before the age of seven based on the hadith "Teach them at seven and discipline them at ten" and the saying "Play with him for seven"?

It is permissible to hold a child accountable for their mistakes, without hitting, at any age where they comprehend the meaning. As for hitting, it should only occur after the age of ten, based on the Prophet's (peace be upon him) saying: "Instruct your children to pray when they are seven years old, and hit them for [not praying] when they are ten years old, and separate them in their beds."