How to transform an empty GameObject that has gameObject children?

I have created an empty gameObject and added child gameObjects from primitives which I reference via a List<>

public class ObjectManager : MonoBehaviour { private List<GameObject> _cubes;

Primitive generation code snippet:-

        for(int i = 0; i < cubesPerRow; i++)
        {
            cube = GameObject.CreatePrimitive(PrimitiveType.Cube);
            cube.transform.position = new Vector3(nextX,nextY,0);
            nextX = (cube.transform.localPosition.x + cube.transform.localScale.x) + cubeSpacing;
            _cubes.Add(cube);
        }

This works fine but now I wish to rotate the parent (objectManager) and have all the child cubes affected by this. To reiterate, I want to apply a single transform and have all of the objects move based on their parents transform.

When I apply a single transform to the parent via Update() none of the children move at all, however I can loop through the _cubes collection and apply transforms to them (which is not the desired behavior).

I am used to Flash's parent / child relationships but new to Unity and 3d so hopefully someone can explain the best way to work with Child objects to me going forward.

Thank you.

[EDIT: Here is my Update function]

    void Update()
{
    float amtToMove = 60.0f * Time.deltaTime;
    transform.Rotate(amtToMove, amtToMove, amtToMove * 2);
}

I have also tried with gameObject.transform to no avail.