When Does a Child Become Obligated to Follow Islamic Rulings?

A boy becomes accountable (mukallaf) when he reaches puberty and is of sound mind. A child reaches puberty when he turns fifteen years old, or when coarse hair grows below the navel, or when semen is emitted through a wet dream or in a state of desire. A girl, in addition to all of these signs, reaches puberty when menstruation begins. But when coarse hair grows around the private parts, or emission with desire begins, even if his age is less than fifteen years, he becomes accountable.
When he reaches puberty, prayer and fasting become obligatory upon him. If he has the financial means, Hajj also becomes obligatory. However, even before that, at the age of seven or older, it is permissible for him to pray and to fast, if he is able to. But if his wealth reaches the nisab (minimum threshold) and a year passes over it, zakah is absolutely obligatory upon him. (Puberty is not a condition for paying zakah.)