Magento does not show configurable product options

Use this below code

Code to get the the full product information (where 3 is the configurable product Id)

$product = Mage::getModel('catalog/product')->load(3); 
$childProducts = Mage::getModel('catalog/product_type_configurable')
                    ->getUsedProducts(null,$product);

foreach($childProducts as $child) {
    print_r($child->getName());  // You can use any of the magic get functions on this object to get the value
}

Another code to get the Children Product Ids

$childProducts = Mage::getModel('catalog/product_type_configurable')
                    ->getChildrenIds(3);

Hope this helps!!

In Magento strictly saying, a Configurable product(CP) is not a product in itself, but a collection of simple products. When you are choosing among 10 colors of a CP is nothing but choosing 10 different simple products of the same color.

Suppose a store have only one RED Ball and two magic boxes CP1 and CP2.

Now you can take out the RED Ball from any of the boxes,as it is a magic box. But when you take out the ball from one of the boxes(CP1), the RED Ball can't be taken out from the other box(CP2) or from the CP1 as there is only One RED Ball.

Now you can have hundreds of Magic Boxes and you can take the RED Ball from any of the boxes(if the magician allows it- in this case store owner), but when the stock of RED Ball is out then nobody can take out the RED Ball from any of the boxes.

And to make the product out of stock when the Quantity becomes zero, you have to go to

System->Configuration->Inventory(under catalog tab)

As shown in the image below, set the field marked in red to zero.

That's it. Hope I made your concept clear about Configurable Product. Enjoy...