If the child had been seen in er & stitched, iodine
was used to clean the wound, which will give a metallic smell.
If not, did the tooth move/change color? Is there a bump above/below it? If the answer is yes to any of these, then the tooth may be infected, causing the odor. If the child has not seen a dentist already, please do, if only to play it safe for the adult tooth growing above/below.