Fade the alpha of all childrens SpriteRenderers?

Hi there,

How do I change the alpha of all my GameObjects children over time? Well not all of them, everyone with a certain tag. Before adding the IEnumerator, I was able to turn the alpha on/off. But I'm struggling with doing it over time.

Current script looks like this:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
 
 public class SeeThroughObjects : MonoBehaviour {
 
     private Color startColor;
     private Color transparentColor;
 
 
     private void Start()
     {
         foreach (SpriteRenderer sr in GetComponentsInChildren<SpriteRenderer>())
         {
             startColor = sr.material.color;
         }
     }
 
 
     void OnTriggerEnter2D (Collider2D other)
     {
         if (other.tag == "Player")
         {
             foreach (SpriteRenderer sr in GetComponentsInChildren<SpriteRenderer>())
             {
                 if (sr.CompareTag("HiddenSprite")) //If It's an object tagged with HiddenSprite, leave as is.
                 {
                     sr.material.color = startColor;
 
                 }
                 else //Make all children that are NOT tagged with Hiddensprite transparent.
                 {
                     //sr.material.color = transparentColor;
                     StartCoroutine(FadeTo(0.0f, 1.0f));
                 }
             }
         }
     }
 
 
     void OnTriggerExit2D(Collider2D other)
     {
         if (other.tag == "Player")
         {
             foreach (SpriteRenderer sr in GetComponentsInChildren<SpriteRenderer>())
             {
                 if (sr.CompareTag("HiddenSprite")) //If It's an object tagged with HiddenSprite, leave as is.
                 {
                     sr.material.color = startColor;
                 }
                 else //Make all children that are NOT tagged with Hiddensprite visible again.
                 {
                     //sr.material.color = startColor;
                     StartCoroutine(FadeTo(1.0f, 1.0f));
                 }
             }
         }
     }
 
 
     IEnumerator FadeTo(float aValue, float aTime)
     {
         float alpha = startColor.a;
         for (float t = 0.0f; t < 1.0f; t += Time.deltaTime / aTime)
         {
             transparentColor = new Color(1, 1, 1, Mathf.Lerp(alpha, aValue, t));
             startColor = transparentColor;
             yield return null;
         }
     }
 
 
 }
 

Thanks in advance!