You can't show/hide a prefab as such, because a prefab is like a "template" of an object which could exist in your scene. You probably want to hide/show a gameobject (which might or might not be an instance of a prefab).

Do do this, you set the GameObject's renderer.enabled property to either true or false, like this:

function Update() {

    if (Input.GetKeyDown(KeyCode.Z)) {
        // show
        renderer.enabled = true;
    }

    if (Input.GetKeyDown(KeyCode.X)) {
        // hide
        renderer.enabled = false;
    }
}

or, to toggle the visibility on and off with a single keypress:

function Update() {

    if (Input.GetKeyDown(KeyCode.Z)) {
        // toggle visibility:
        renderer.enabled = !renderer.enabled;
    }
}

If you need to change the visibility of a GameObject and its children, you can loop through every object and change each one, like this:

function Update() {
    if (Input.GetKeyDown(KeyCode.Z)) {
        ToggleVisibility();
    }
}

function ToggleVisibility() {
    // toggles the visibility of this gameobject and all it's children
    var renderers = gameObject.GetComponentsInChildren.();
    for (var r : Renderer in renderers) {
        r.enabled = !r.enabled;
    }
}

(moved the toggling code to a separate function, which is often a good idea once any particular section of code starts growing significantly in size)

Whit C# to disable Textures I use this code:

public void ChangeMenuActivity(bool state)
{
    ToggleVisibility(gameObject.transform, state);
}

void ToggleVisibility(Transform obj, bool state)
{
    for (int i = 0; i < obj.GetChildCount(); i++)
    {
        if (obj.GetChild(i).guiTexture != null)
            obj.GetChild(i).guiTexture.enabled = state;
        if (obj.GetChild(i).guiText != null)
            obj.GetChild(i).guiText.enabled = state;

        if (obj.GetChild(i).GetChildCount() > 0)
        {
            ToggleVisibility(obj.GetChild(i), state);
        }
    }
}

Tambien se puede hacer de la siguiente forma:

using System.Reflection;

void OcultarPadreHijos(object objGO) {

 PropertyInfo Propiedad= objGO.GetType().GetProperty("enabled");

 Propiedad.SetValue(objGO,false,null);

}

Si quieres ocultar a sus componentes hijos, solo mandas a llamar a la función por cada hijo