It is recommended that you would get at least the Adult's or Giant's Wallet before doing this. In Zora's Domain, go to the top of the waterfall as a child and talk to the Zora there. Accept the mini-game and he will throw Rupees in the water below. Rarely, if you are lucky, he will throw an Orange Rupee worth 500 Rupees. Keep playing the mini-game at anytime if you want the Orange Rupee again.