Hello,
Unfortunately in all amimal species there is the possibility of a conflict between males of the species for dominence. This is what I am afraid is happening with your two gerbils. Many times this becomes a territorial issue and one or both of the Gerbils can be injured. My suggestion would be two separate enclosures to keep the two males on their own. This will alleviate the problems of possible injury to one or both of them. You can keep them close by one another, but with independant enclosures they should calm down and even become better pets for your son. Joan
http://members.nanc.com/~mhaines/gerbil.html#section2.2