Transform child out of bounds

Hey Guys, I have some trouble with the error message "transform child out of bounds".... In my project I have a switch-case to look which objcet has been choosen and what the user wants to do with it. The object will be initiated via mouse click.

Case 1 works perfectly but case 2 shows the error message... Hopefully, I can get some help :-)

Here is my code:

     findMychild = transform.Find("WeldContent/Schweißnaht " + ButtonActionManager.PosValue).gameObject;
     
             //Referenz erzeugen zur Klasse SavePath um die Funktion RemoveListElements aufzurufen
             GameObject gone = GameObject.Find("StreamingClient/Table_KS/TCP");
             SavePath vas = (SavePath)gone.GetComponent(typeof(SavePath));
     
             if (ButtonActionManager.ButtonStatus == false)
             {
     
                 //Debug.Log("Status: false");
                 switch (ButtonActionManager.PosValue) //DropdownPrefab.value
                 {
                     //Default -Bitte Auswählen-
                     case 0:
                         Debug.Log("keine Auswahl getroffen");
                         break;
     
                     //Auswahl 1
                     case 1:
                         Debug.Log("Auswahl 1");
                         //Wenn der Button für Highlight gedrückt wurde
                         if (ButtonInteraction.Highlight == true)
                         {
                             if (Color == true)
                             {
                                 Debug.Log("Coloer == true");
                                 for (int k = SavePath.Trajektory.Count - 1; k >= 0; k--)
                                 {
                                     if (SavePath.Trajektory[k].SchweißNahtNo == ButtonActionManager.PosValue)
                                     {
                                         rend = findMychild.transform.GetChild(k).GetComponent<MeshRenderer>();
                                         rend.sharedMaterial = Material;
                                         
                                     }
                                 }
                                 Debug.Log("Set Color false");
                                 Color = false;
                             }
                             else if (Color == false)
                             {
                                 Debug.Log("Coloer == false");
                                 for (int k = SavePath.Trajektory.Count - 1; k >= 0; k--)
                                 {
                                     if (SavePath.Trajektory[k].SchweißNahtNo == ButtonActionManager.PosValue)
                                     {
                                         rend = findMychild.transform.GetChild(k).GetComponent<MeshRenderer>();
                                         rend.sharedMaterial = OtherMaterial;
     
                                     }
                                 }
                                 Debug.Log("Set Color true");
                                 Color = true;
                             }
                             
                         }
     
                         //Wenn Auswahl Delete getroffen ist dann destroy parent GameObject
                         if (ButtonInteraction.Delete == true)
                         {
                             Debug.Log("Auswahl Delete getroffen");
                             //aufrufen der Funktion RemoveListElements
                             vas.RemoveListElements();
     
                             Debug.Log("findMychild zerstören");
                             //Zerstören des GameObjects findMychild
                             Destroy(findMychild);
                         }
     
                         //Wenn Auswahl Activate/Deactivate getroffen ist Activiere/Deaktiviere das GameObject
                         if (ButtonInteraction.Visibility == true)
                         {
                             findMychild.SetActive(false);
                         }
                         break;
     
     

case 2 is excacly the same!