In one of our projects, the requirement was to have a different layout for some category pages. So, we decided to use a different template file for these categories. We added the following code in the “Custom Layout Update” field for these categories in admin.
 

 <reference name="category.products">
    <action method="setTemplate">
        <template>catalog/category/custom-category.phtml</template>
    </action>
</reference>

These category pages need to show the products in a different layout.

We can get the category object in the “custom-category.phtml” file as shown below and access the category data.

$_category  = $this->getCurrentCategory();

Now the next step was to get the category products collection.

The layout handle “catalog_category_default” has the following code

<catalog_category_default translate="label">
        .
        .
        .
        <reference name="content">
            <block type="catalog/category_view" name="category.products" template="catalog/category/view.phtml">
                <block type="catalog/product_list" name="product_list" template="catalog/product/list.phtml">
                    .
                    .
                    .
                
                </block>
            </block>
        </reference>
    </catalog_category_default>

So the need was to get child block “product_list” in the “custom-category.phtml” file

Here is the code that I used get the child block and load the product collection

<?php
    $productBlock = $this->getChild('product_list');
    $_productCollection = $productBlock->getLoadedProductCollection();
?>

Summary

1.  You can use the “getChild()” method defined in {{MAGENTO_ROOT}}app/code/Mage/Core/Block/Abstract.php to retrieve child block by name.
2. If you pass the block name like “$this->getChild(‘product_list’)” it returns that block object.
3. If you do not pass anything to the “getChild()” method it returns all the child blocks.
4. $this->getChildHtml() returns the html content of all child blocks