What is the ruling on paying zakat on money saved in a piggy bank during childhood, and what is its nisab if it becomes obligatory?

Zakat is obligatory on the minor's wealth if it reaches the nisab (minimum threshold), and his guardian must pay it. This is the view of the majority of scholars. They cited as evidence the Prophet's (peace be upon him) saying: "Verily, whoever is a guardian of an orphan who has wealth, let him trade with it and not leave it until charity consumes it." Zakat is a right related to wealth, and the minor and the insane are among those who are eligible for reward and solace.