My son spent my money on in game app and want to somehow cancel it

Sales are typically final but take a look at this:

How to report an issue with Your iTunes Store purchase

http://support.apple.com/kb/HT1933

iTunes Purchase Problems: How to Report a Problem to iTunes Support

http://tinyurl.com/7tscpa7

How to Get a Refund from the App Store

http://gizmodo.com/5886683/how-to-get-a-refund-from-the-app-store

Getting Refunds for your iTunes Store Purchases

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

Canceling a Digital Subscription

http://gadgetwise.blogs.nytimes.com/2011/10/14/qa-canceling-a-digital-subscripti on/

All you can do is contact the developers and see if they will give you a refund. Ther terms in the app store are that all sales are final, so they don't have to, but sometimes they do.

To help with future issues you may want to go into the settings and restrictions (which will prompt you to set a passcode) and turn in app purchases off. You can also go into the App store tab and set the 'require password' from 15 minutes to Immediately. Both of these settings help to prevent accidental purchases....as long as the person in question doesn't have the apple ID password or restrictions passcode.

You can try contacting apple support at 1-800-APL-CARE. Have all your account and product into handy.