ChangeMaterialChildrenCleaned

using System.Collections.Generic;
using System.Linq;
using UnityEngine;

//This attribute is used so the component is working in also Edit Mode  (not in play)
[ExecuteInEditMode]
public class ChangeMaterialChildren2 : MonoBehaviour
{
    //Class to simplify the visualization on inspector window
    [System.Serializable]
    private class MeshMaterial
    {
        public MeshRenderer targetMeshRenderer;        //Target meshRender to apply targetMaterial
        private Material targetMaterial;                //Target maaterial to apply to meshRenderer
    }

    public Material masterMaterial;

    [SerializeField]
    private List<MeshMaterial> meshMaterial;  //List of combination of MeshRenderer - Targetmaterial

    [SerializeField]
    private bool updateAll = false;           //Used on inspector to update all meshRenderer in the list meshMaterial

    private void Update()
    {
        //When you check the box (uptadeAll)
        if (updateAll)
        {
            //apply all the materials
            foreach (var m in meshMaterial)
                m.targetMeshRenderer.sharedMaterial = masterMaterial;       //changed to update from masterMaterial

            //Reset updateAll, otherwise this is called every frame (not ideal)
            updateAll = false;
        }
    }

    //This is called when you attach this component on a gameObject, so I use it to initialize
    private void Reset()
    {
        meshMaterial = new List<MeshMaterial>();

        //I assume that your "carpets" are 3D models, so i'll search all children items of this gameobject with MeshRenderer component.
        List<MeshRenderer> mr = GetComponentsInChildren<MeshRenderer>().ToList();

        //If i recall correctly GetComponentsInChildren will include the parent (this gameobject) so i remove the parent
        MeshRenderer myMeshRenderer = GetComponent<MeshRenderer>();
        if (myMeshRenderer != null)
            mr.Remove(myMeshRenderer);
    }
}