I can addChild movieClip using check box, but how do you removeChild when box is unchecked?

I will have 8 check boxes on this screen. I want the user to check any number or all boxes to see a line on a graph. I also want them to be able to uncheck the selected box to remove the line. Each box calls a certain line to the stage.

I can get the line to show up when checked, but not dissappear when unchecked.

I also want to have a check box to select all lines on the screen.

var graph:hp455mt_mc = new hp455mt_mc();

box455.addEventListener(MouseEvent.CLICK, clickHandler);

function clickHandler(evt:MouseEvent):void {

  addChild(graph);
graph.x = 179;
graph.y = 22.35;     
}