I put money on the wrong xbox account and want to transfer it

Unfortunately there is not anyway to do this.

You can sign into that account and make a gift purchase for the item that your son wanted for his other account. This would be the only way to do this

Sadly you cant transfer it over but if you want to buy a game or some type of ad on it will be something called buy as a gift under buy and you can send it to that account but some ad on wont let you do it but games 100% will

The problem is that account is completely dead. We don't even know how to login and can't reset the password because there were no validations put in for resetting password when it was set up.

I have put money onto the wrong xbox account. Is there anyway of switching this onto an account i actually use

Unfortunately not. No. Nothing is transferable between accounts.

You would have to try contacting support and speak to billing, but generally it is not possible to transfer funds between accounts. 1-800-4my-xbox if you're in the US/Canada or http://support.xbox.com/contact-us