WHAT IS THE 'CHILD OF ALL'?

"A MAP?" Argent repeated.

"Yes.  The image was a bit blurry and it only lasted for about five seconds, but I'm sure it was a map," Aurum confirmed.

An image of a map that appeared after Aurum's blood came into contact with the pendant.  Now, why did it sound so familiar?  Because that's almost like what happened when Argent tried to enter the dragon king's temple.  

"That map will probably lead us to the location of one of the remaining two artifacts."

Aurum frowned a bit.  "How can Brother be so sure?" she asked, because the way Argent said it, it's like she had no doubt that the map would definitely lead them to the location of either of the two artifacts.