Get components in children and childrens children and so on

Edit: Just use GetComponentsInChildren()

 public static class Extension
     {
         public static List<T> GetComponentsInChildrenRecursively<T>(this Transform _transform, List<T> _componentList)
         {
             foreach (Transform t in _transform)
             {
                 T[] components = t.GetComponents<T>();
     
                 foreach (T component in components)
                 {
                     if (component != null)
                     {
                         _componentList.Add(component);
                     }
                 }
     
                 GetComponentsInChildrenRecursively<T>(t, _componentList);
             }
     
             return _componentList;
         }
     }

To use this do something like this:

 public Transform parent;
     
     public void Example() {
         List<Transform> transformList = new List<Transform>();
         parent.GetComponentsInChildrenRecursively<Transform>(transformList);
         //use transformList as you wish
     }

Cheers, Michael