I am generating many cubes during runtime and applying some photos to them (it's a type of VR photo browser). Anyway, I am trying to encapsulate them all in a larger cube using the smallest possible bounding box of all the little cubes. This is what I have so far.

After generating all the cubes, the first thing I do is center them all on their parent so the user can position and rotate them relative to the center.

     Transform[] children = GetComponentsInChildren<Transform>();
     Vector3 newPosition = Vector3.zero;
     foreach (var child in children)
     {
         newPosition += child.position;
         child.parent = null;
     }
     newPosition /= children.Length;
     gameObject.transform.position = newPosition;
     foreach (var child in children)
     {
         child.parent = gameObject.transform;
     }

Then I calculate the bounds of all the cubes which are children of the parent.

     Renderer[] meshes = GetComponentsInChildren<Renderer>();
     Bounds bounds = new Bounds(transform.position, Vector3.zero);
     foreach (Renderer mesh in meshes)
     {
         bounds.Encapsulate(mesh.bounds);
     }
     Bounds maximumScrollBounds = bounds;

Then I create the new larger (red/transparent) cube which will encapsulate all the smaller ones and use the bounds I previously calculated for it's scale.

     GameObject boundingBox = GameObject.CreatePrimitive(PrimitiveType.Cube);
     Destroy(boundingBox.GetComponent<Collider>());
     boundingBox.GetComponent<Renderer>().material = Resources.Load("Materials/BasicTransparent") as Material;
     boundingBox.GetComponent<Renderer>().material.color = new Color32(255, 0, 0, 130);
     boundingBox.name = "BoundingBox";
     boundingBox.transform.localScale = new Vector3(maximumScrollBounds.size.x, maximumScrollBounds.size.y, maximumScrollBounds.size.z);
     boundingBox.transform.localPosition = maximumScrollBounds.center;
     boundingBox.transform.SetParent(transform); 

But the problem is the encapsulating cube is always slightly too big and I cannot figure out why.

I need it to basically only reach the very edges of the smaller cubes inside of it.