As above, the ship is on a cashless system; everything is billed to the KTTW card. You can take the cash to GS and apply it to her account, but that requires her to have charging and for an adult to sign for financial responsibility for her. There is no way to limit kid charging--they either have it or they don't.
It gets even more complicated--if you book any excursions thru
DCL for your child, they will show up on the child's account (even though YOU planned to pay for them. The only way around this is for you to pay off the excursion amount before the child sees it and freaks out over the big amount that she didn't spend.
Kid doesn't need money or charging for the arcade. You can use your KTTW to purchase an arcade card and when it runs out the child needs to see you to get it reloaded. Or go to the arcade when the programming is doing "Invade the Arcade" as all the machines are set to free play then.
Nothing done in the programming has a charge, including things that would be charged at other times. For instance, if they do "Into the Blender" or "smoothie Party," each kid participating at that time gets a free smoothie. If they do "make a t-shirt," they get a free shirt to use. When DD made a picture frame, Captain Mickey came and each kid had a photo taken. They then got the photo free (from the Oceaneer's club, not from Shutters). I don't think they do the picture frame thing any more though.