By opening the Heart Piece Chest located at Gerudo's Fortress as Child Link, you will get an Odd Mushroom instead of a Heart Piece.
If you save/quit the game it will revert back to Cojiro since the game iterprets it as failing the timed trading sequence. If you show this Cojiro to the guy with the Odd Mushroom, he will trade for it.
Requirements: Bottled Bugs/Fish, Bottle on B & Green Potion
If you perform this to get the Spirit & Shadow medallion before turning into adult for the first time, the Light Arrow cutscene trigger instead of Sheiks Introduction cutscene. This makes it possible to skip Sheiks Intro cutscene unless you enter the Pedestal Room, which triggers it.
Combining this with Magical Arrows as Items makes it possible to beat Ganondorf without entering any Adult Temples, or starting the Adult Link Trade Sequence.