Is zakat obligatory on a son's gold purchased with money received as a gift (nuqut), and does zakat consume wealth if the gold is dormant and not being utilized?

The minimum threshold (nisab) for zakat on gold is 85 grams of pure gold. The gold you bought for your son is not subject to zakat because it has not reached the nisab. However, if a child's wealth reaches the nisab and a full year (hawl) passes, then zakat becomes obligatory on it, even if it is stagnant wealth. This is why it is permissible to invest the wealth of orphans so that zakat does not deplete it. It is not permissible for a male child to adorn himself with gold.