How is possible add child to the specific node

Question

This is my starting xml :

 
    
      
        
     &         


        

Answer 1

With DOMDocument it's as easy as this:

$child = new DOMElement('children');
$parent->appendChild($child);

Whereas $parent is the DOMElement parent which (after you have updated your question) to aquire is part of your problem:

// append  to the first  element
$parent = $dom->getElementsByTagName('child')->item(0);
$child = new DOMElement('children');
$parent->appendChild($child);