Problem with parented arm/upperbody box/collision box

Im making a first shooter game and this is my first try making a game.
so, i made this gun with two arms and upper body box to look up and down using mouse,
and a collision box to move and look left right by using mouse.
but weirdly, in game, when i move my mouse to turn aside, those three things gets apart like it is bounded to a certain spot.
this thing is really knocking me out… any comment will be appreciated :]

What is parented to what?
Have you applied scale and rotation to each objet (<ctrl+a>) ?

Your images are not telling very much.

You might have a look at the FPS templates in the Resource forum.