ChangeMaterialChildren

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 ChangeMaterialChildren : MonoBehaviour
{
    //Class to semplify the visualization on inspector window
    [System.Serializable]
    class MeshMaterial
    {
        public MeshRenderer targetMeshRenderer;        //Target meshRender to apply targetMaterial
        public Material targetMaterial;                //Target maaterial to apply to meshRenderer
        public bool updateMaterial;                    //Used on inspector window to apply targetMaterial on meshRenderer
    }

    [SerializeField]
    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


    void Update()
    {
        //When you check the box (uptadeMaterial) in the inspector of an item in the meshMaterial list
        MeshMaterial itemToUpdate = meshMaterial.Find(m => m.updateMaterial == true);
        if (itemToUpdate != null)
        {
            itemToUpdate.targetMeshRenderer.sharedMaterial = itemToUpdate.targetMaterial;             //Applying material to meshRenderer
            //Setting to false again because we already applied to material
            //other wise this is called every frame (not ideal)
            itemToUpdate.updateMaterial = false;
        }

        //When you check the box (uptadeAll)
        if (updateAll)
        {
            //apply all the materials
            foreach (var m in meshMaterial)
                m.targetMeshRenderer.sharedMaterial = m.targetMaterial;


            //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
    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);

        //Initializing the list of MeshRenderers affected
        foreach(var r in mr)
        {
            MeshMaterial meshMat = new MeshMaterial();
            meshMat.targetMeshRenderer = r;
            meshMat.targetMaterial = r.sharedMaterial;  //By default the targetMaterial is the current material of the mesh renderer
            meshMat.updateMaterial = false;

            meshMaterial.Add(meshMat);
        }
    }
}