How to get child categories in Magento

Sometime you may want to get the child categories from a specified category Id. There is a way to do that

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public function getItems() {     $categoryId = 3;     $category = Mage::getModel('catalog/category')->load($categoryId);     $children = $category->getChildrenCategories();     $items = array();     foreach ($children as $child)     {         $item = new stdClass();         $item->name = $child->getName();         $item->link = $child->getUrl();         $items[] = $item;     }           return $items; }