Child sku

config.xml

<?xml version="1.0" encoding="UTF-8"?>
<config>
    <modules>
        <Demac_Childsku>
             <version>0.0.1</version>
        </Demac_Childsku>
    </modules>
    <global>
       <models>
           <childsku><class>Demac_Childsku_Model</class></childsku>
       </models>
    </global>
    <crontab>
            <jobs>
                <demac_childsku_add>
                    <schedule><cron_expr>1 1 * * *</cron_expr></schedule>
                    <run><model>childsku/observer::addChildSkus</model></run>
                </demac_childsku_add>
            </jobs>
    </crontab>
</config>

Demac_Childsku

<?xml version="1.0"?>
<config>
    <modules>
        <Demac_Childsku>
            <active>true</active>
            <codePool>local</codePool>
        </Demac_Childsku>
    </modules>
</config>

Observer.php

class Demac_Childsku_Model_Observer
{
    public function addChildSkus()
    {
        $productConfig = Mage::getResourceModel('catalog/product_collection')->addAttributeToFilter('type_id', 'configurable');
        foreach ($productConfig as $parent){
             $singleConfig = Mage::getModel('catalog/product_type_configurable')->setProduct($parent);
             $simpleCollection = $singleConfig->getUsedProductCollection()->addAttributeToSelect('*');

             foreach($simpleCollection as $simple){
             //Do something here to modify your parent product.
             }
        }
    }
}