Originally posted by gorickey:
You can change his account password yourself since you are an admin...if you don't want your son changing the password, then don't make him an admin user....
ANY user can change their own password! An admin user is not supposed to be able to look at other user's files, however root can.
You can sudo -s (in terminal) to switch to the root user who can do anything.
You could enable to root user and log in as root (GUI) and then do anything. However, this is not recommended.
NB: You can do nasty damage to your system as root if you don't know what you're doing.
You could temporarily change the permissions on his directories to see what's in there... Get Info, authenticate, change permissions. Although I'm not sure if this works on another users files, it may work as an admin (authenticating as admin is this situation, effectively does a sudo and gives you root privileges for that operation).