I apologize. I must have confused what you were saying with the requested prizes.
You can delete the purchased item by clikcing the "Add/Edit Prizes" button in the left navigation. You will then need to add the point value back to your child's account. I am going to make note of this on our to-do list as this is not a very convenient method to reverse things when prizes are accidentally purchased. There should be a much smoother way to revert back.
Thank you for bringing this to my attention.
Susan