Is zakat obligatory on money saved for one's son, what is its zakat threshold (nisab), and how is zakat calculated—on the principal amount saved or on the profits if it is invested, and what is the nisab for each?

Scholars have differed regarding the obligation of zakat on the minor's wealth, and the more preponderant opinion is that it is obligatory, with his guardian being responsible for it. The minor's guardian must pay zakat on his wealth if it reaches the nisab (minimum threshold). The nisab for currencies is determined by their value in gold or silver. Zakat is obligatory on trade goods if they reach the nisab and a full year has passed over them, and this includes both capital and profit. Scholars have differed on when the zakat year for trade goods begins if their capital did not initially reach the nisab.