Child BA (Bottle Adventure) is a method of putting any item that can be BA'd onto child link's B button. This allows you to defeat volvagia as child, skip the mask trading sequence by getting bunny hood on b and selling it, and using RBA and BA with the broken Goron's Sword as child. It requires quite some set up to perform.
This is similar to the method used as adult to get deku stick on B from Lon Lon Ranch. There are two main differences for this method. One is that Hammer (Item 17) is set to Temp B instead of 0 (Deku Stick). The other difference becoming swordless from Ganon instead of a horse. The logic for temp b being restored to b works like this: dying with a non-sword item on b always restores temp b, unless temp b is 0 or 255, in which case B goes to 255 or 0, depending on if the sword flag is set. The sword equipped flag does not affect this trick.
You must open the mask shop by showing Zelda's Letter to the guard in kakariko village. Next, place the Bunny Hood (item 39) on child link's B button as described above and sell it to the running man in Hyrule Field. You will need to mash B then talk