You need shadow to define edges. That photo is far too overexposed to save as it is. See if you can recover any details from RAW file, and follow what Ershin said above. What he's saying is basically if you can find the details in RAW file, you can lay that on top of what you have, and mask out the bits you want to keep in your current shot.
Quite frankly, since it's your nephew, you'll have more opportunities. Put it down to experience, and retry next time you see him, and try to light him better. Remember, you need to light at an angle to create shadow, which gives it depth and definition.
Good luck