It is possible to restrict access to your Xbox LIVE account by using a pass code, or making it necessary to sign into your Xbox profile using your Microsoft account password.
Set a pass code
A pass code is a button sequence on your controller, which you can use to restrict access to your Xbox LIVE profile. After you have set the pass code, anyone who wants to sign into Xbox LIVE using your profile must enter the pass code.
Steps to follow
1) Under Settings, select Account
2) Go to Account Security, and then select Pass Code
3) Enter your four-button code on your controller. You can use the directional pads, the triggers, the bumpers, X and Y.
4) Re-enter your pass code for confirmation
The next time you sign in with your Xbox LIVE gamertag, you will be required to enter the pass code.
If you want to change or reset your pass code, just repeat the above steps. You will be required to enter the old pass code before you can change it.