Access of undefined property ERROR

I have a piece of code that adds a child through a sprite, I am now trying to access that child by doing SPRITE_NAME.CHILD.PROPERTY (blockholder.stoneblock.myProperty)

But I get this error:

BlockHolder.as, Line 14    1120: Access of undefined property stoneblock.

Here is my code where I try to access stoneblock

package  {
    
    import flash.display.Sprite
    
    public class BlockHolder extends Sprite {

        public function BlockHolder() {
            
            
        }
        
        public function checkScroll():void
        {
            stoneblock.checkScroll();
        }
        
    }
    
}

And here is where I add stoneblock to blockholder:

var dirtblock:DirtBlock = new DirtBlock();
                var stoneblock:StoneBlock = new StoneBlock  ;
                if (blockY >= 9)
                {
                    checkCave();
                    if (Global.vars.cave == true)
                    {
                    }
                    else
                    {
                        stoneblock.x = i * 10;
                        stoneblock.y = blockY * 10 - 10;
                        blockholder.addChild(stoneblock);
                        listofblocks = stoneblock.x + "," + stoneblock.y;
                    }
                }
                else
                {
                    dirtblock.x = i * 10;
                    dirtblock.y = blockY*10 - 10
                    ;
                    blockholder.addChild(dirtblock);
                    
                    listofblocks = dirtblock.x + "," + dirtblock.y;

                }

                if (i == 100 && blockY < 100)
                {
                    blockY++;
                    i = 0;
                    gamescroll.update();
                }

I also tried doing blockholder.stoneblock.myProperty through the game.as, but that didn't work.

I am trying to do things to these blocks, and am needing someone to point me in the right direction, any help would be greatly appreciated.