If your son can't remember his pass code, the only option is to use iTunes to erase the iPad and restore it to factory condition. If the backup was made after the password was added to the iPad, it can't be used, as it will just put the password back on the iPad. Your son will have to set it up as a new iPad and can use his iTunes and AppStore purchased lists to restore his purchases to the iPad.
I"m not sure this is quite right scifan57. The passcode which is set on your device is NOT saved as part of the standard backup. The FACT that a passcode was active is known, but the passcode itself is not saved.
Consider the situation where you back up your device today, then change your iPad passcode every day for the next 10 days without another backup. You do NOT have to remember the passcode which was set 10 iterations ago when you originally took your backup in order to restore it. If people had to remember which passcode was active for each backup that was taken, then lots of folks would be in one heck of a mess very often
It is for this very reason that there are several security options around backups...
1) if you use iTunes to save your backup, you are offered the option to encrypt the backup file on the PC with a completely separate password (ironically, folks do forget the password they set here quite often)
2) if you use iCloud, your backup (and everything else stored there) is protected by your AppleID and password credentials combination.
@alandalaney, if you restore the device using iTunes to factory fresh IOS 6.1.2, and provided you have the AppleID and associated password, you will be able to restore the iCoud backup for the device without needing to know the passcode that was active on the device when it was taken.