You are looking at the HTML representation of the XML format.
HTML is good for debugging, but is unsuitable for application use.
Specify the format parameter to change the output format.
To see the non HTML representation of the XML format, set format=xml.
See the complete documentation, or API help for more information.
<?xml version="1.0"?>
    <alltransclusions gatcontinue="Birth_date_and_age|138" />
      <page pageid="94" ns="0" title="Chelsea Under-18s" />
      <page pageid="97" ns="0" title="Chelsea Under-21s" />
      <page pageid="104" ns="0" title="Arsenal Under-18s" />
      <page pageid="105" ns="0" title="Arsenal Under-21s" />
      <page pageid="108" ns="0" title="Manchester City Under-21s" />
      <page pageid="113" ns="0" title="Everton Under-18s" />
      <page pageid="114" ns="0" title="Liverpool Under-18s" />
      <page pageid="115" ns="0" title="Manchester United Under-18s" />
      <page pageid="116" ns="0" title="Sunderland Under-18s" />
      <page pageid="136" ns="0" title="Fulham Under-18s" />