drawRect() Paradox

Hello gurus!

While using addChild() method for populating children inside a rectangle Sprite; if I use:

mySquare.graphics.drawRect(250, 35, 175, 175);

instead of:

mySquare.graphics.drawRect(0, 0, 175, 175); 
mySquare.x = 250; 
mySquare.y = 35;

it makes a lot of difference. In first case, the following statements cause all the children fall outside the parent mySquare Sprite, whereas they fall inside the parent in the second case.

myCircle.graphics.beginFill(0xFFCC00); 
myCircle.graphics.drawCircle(50, 50, 50); 
square.addChild(myCircle);

I just want to understnad why is it like that. Any help, please!