I have a purchase from my son and can't get a refund from it

You can contact iTunes support to see if you can. Go expresslane.apple.com and click on iTunes in the middle. Then click on iTunes Store. Then youll see options and take it from there until you see either a Chat or an Email and you can ask for a refund that way.

Return your iTunes Store Purchases to Apple

The iTunes App store sales policy clearly says that you cannot cancel a purchase or receive a refund for a purchase but they are known to make exceptions if you have a valid reason.

For instance, I recently purchased the $2.99 Reeder app from the iTunes store but only after installing it on my iPad did I realize that it was an iPhone-only app and not designed for the iPad. I requested a refund from Apple and how they reversed the charges in less than 4 hours.

Step 1: Locate the email receipt for your iTunes Store purchase and click the “Report Problem” link next to the app that you would like to return.

If you have deleted the email invoice that Apple sent you after you completed the purchase, launch the iTunes program using this special link and you’ll see a list of all items that you’ve bought from the iTunes store. Open an order by clicking that little arrow next to the order date and then click “Report a problem” next to the app name.

If the above method fails, or if you don’t have iTunes on your computer, you can use this pageto submit a refund request to Apple through any web browser.

Step 2: Click the Problem drop-down menu and choose an option that best describes your problem. If you have purchased an app accidentally, choose “I inadvertently purchased this application.”

You can expect a response from Apple in the next 24-48 hours. If the support rep is satisfied with your reasoning, he’ll probably reverse the charges. Please remember that you are not entitled to a refund under the iTunes Store Sales policy so if they deny your request for a refund, move on!

Retrieved from http://www.labnol.org/software/itunes-app-store-refunds/13838/

Cheers.

Go to Utilities > Settings > Restrictions and Turn off all of the items (iTunes, Bookstore, Installing Apps, In App Purchases, etc.) that you do not want your son to use to avoid this problem in the future.