character push and drag box

Hi all!

I'm playing with the 2d platform environment and I'm trying to modify the "platformer push body" with the "drag" option. I want to push and drag the object only when a button is pressed and when the button is released the object is not more dragged (or pushed). When the object is not pushed or dragged it turns into a "non movable" object. I found some tips there about "parenting" the character and the object while dragging and release it when the drag (release the button in my case) stops.

Here is my code:

if(Input.GetButton("Fire1"))
{
body.transform.parent = gameObject.transform; 
}
else
{
body.transform.parent = null;
}

At the appearence it works but the object physics often go crazy :(

Maybe I need to manage with the transforms of both character and object.

Tnx!