Your password isn't on your son's account. You have to log in with your password to make any changes to his account like permissions and all, but unless you said "always stay logged" in on Xbox.com, your password shouldn't be there. If you want to change
your son's password, then you can do that. Need more information though as to what exactly you are talking about. But you can also try calling support or tweet to "xboxsupport" and they should help.
It could be the settings you have. If you have it set up that you need to approve when he adds a friend, then you can just go in to his profile and change it so that friend requests are allowed etc. Not sure how old your child is, but xbox lets you promote
your chld to an adult account when they turn 18. Prior to that, you can make their child account pretty open just by adjusting the settings in his profile under online safety.
Make sure permissions are set correctly on your account. Log into the child account and change the password. Then you have to verify you are you. Done. (Little more complicated, but those are the steps.)