Transform Child Out of Bounds Error

Hello everyone, Could you help me find the error in my code that results in the "UnityException: Transform child out of bounds" error.

Here is the faulty line of code as well as unity gameobjects:

 private IEnumerator GoByTheRoute(int routeNum)
     {
         coroutineAllowed = false;
 
         Vector2 p0 = routes[routeNum].GetChild(1).position;
         Vector2 p1 = routes[routeNum].GetChild(2).position;
         Vector2 p2 = routes[routeNum].GetChild(3).position;
         Vector2 p3 = routes[routeNum].GetChild(4).position;
 
         while (tParam < 1)
         {
             tParam += Time.deltaTime * speedModifier;
 
             objectPosition = Mathf.Pow(1 - tParam, 3) * p0 + 3 * Mathf.Pow(1 - tParam, 2) * tParam * p1 + 3 * (1 - tParam) * Mathf.Pow(tParam, 2) * p2 + Mathf.Pow(tParam, 3) * p3;
 
             transform.position = objectPosition;
             yield return new WaitForEndOfFrame();
         }
 
         tParam = 1f;
 
         routeToGo += 1;
 
         
 
 
 
     }