how to access child components of the panel? unity

Question

Im getting this Error in this statement Im trying to get image object in Dropzone area all scripts are attached to the editor. I already checked them .I couldnt find problem please help. Error image

     public void CardDetect()
    {
        D = new DropZone();


        List<Image> listofcard = new List<Image>();

for (int i = 0; i<D.transform.childCount - 1; i++)
        {
            if (listofcard != null)
            {
                listofcard.Add(D.transform.GetChild(i).transform.GetComponents<Image>()[i]);

            }

        }

        for(int i = D.transform.childCount - 1; i > 0; i--)
        {
            // this.PlaceholderParent.transform.Find("Pane").GetComponent<Image>().tag = "ileri"
            if (D.transform.GetChild(i).transform.name == "ileriprefab1")
            {
                ileri = true;
            }


            if (D.transform.GetChild(i).transform.name == "sağprefab")
            {

                sağ = true;

            }
            if (D.transform.GetChild(i).transform.name == "solprefab")
            {
                sol = true;
            }

            if (D.transform.GetChild(i).transform.name == "fprefab")
            {

                f = true;
            }




        }

Blockquote Dropzone Script