How to change material color to a specific object group's childs..?

This is the script I am currently Using.

I am trying to change all the child of the object group's color on a specific material.

This is what I have.

 public Transform target;
     
 public Texture2D colorPicker;
 private Texture2D styleTexture;
 
 public int textureWidth = 100;
 public int textureHeight = 100;
 public bool useDefinedSize = false;
     
 public int positionLeft = 0;
 public int positionTop = 0;
 public bool useDefinedPosition = false;
 
 public Color setColor;
 
 public bool showPicker = false;
 
 void Awake() {
     //If size is not using defined size, resize to Texture Size.
     if (!useDefinedSize) {
         textureWidth = colorPicker.width;
         textureHeight = colorPicker.height;
     }
     //If position is not using defined position, relocate to center of screen.
     if (!useDefinedPosition) {
         positionLeft = (Screen.width / 2) - (textureWidth / 2);
         positionTop = (Screen.height / 2) - (textureHeight / 2);
     }
     //Set up color preview box.
     styleTexture = new Texture2D(1, 1);
     styleTexture.SetPixel(0, 0, setColor);
 }
 
 void OnGUI(){
     //If picker is disabled, early return.
     if (!showPicker)return;
         //Color canvas.
         if (GUI.RepeatButton(new Rect(positionLeft, positionTop, textureWidth, textureHeight), colorPicker)) {
             //Get Mouse Position.
             Vector2 pickpos = Event.current.mousePosition;
             int canvasX = Convert.ToInt32(pickpos.x);
             int canvasY = Convert.ToInt32(pickpos.y);
             //Reposition Mouse input according to size and position of the canvas.
             Color col = colorPicker.GetPixel(((canvasX-positionLeft)*((colorPicker.width/textureWidth))),(colorPicker.height-((canvasY-positionTop)*(colorPicker.height/textureHeight))));
             //Return picked color.
             Debug.Log(col);
             //Set Color for display.
             setColor = col;
             }
         //Apply button.
         if (GUI.Button(new Rect(positionLeft + textureWidth - 60, positionTop + textureHeight + 10, 60, 25), "Apply")) {
             //Change material color of all child in the target object.
             foreach(Renderer r in target.parent.GetComponentsInChildren()) {
                 foreach(Material M in r.materials) {
                 M.color = setColor;
                     }
             }
             //target.renderer.material.color = setColor;
             // hide picker
             showPicker = false;
         }
             //Create Style for color preview.
             GUIStyle style = new GUIStyle();
             //Update Color for color preview.
             styleTexture.SetPixel(0, 0, setColor);
             styleTexture.Apply();
             style.normal.background = styleTexture;
             GUI.Box(new Rect(positionLeft + textureWidth + 10, positionTop + textureHeight + 10, 30, 30), new GUIContent(""), style);
         }
 }

I get this error :

 Assets/Scripts/ColorPicker.cs(59,61): error CS0411: The type arguments for method `UnityEngine.Component.GetComponentsInChildren<T>()' cannot be inferred from the usage. Try specifying the type arguments explicitly

How do I fix this..? Can anyone point out my mistakes?