Kenny's dinosaurs always seem to disappear when he plays with LJ Jones. LJ is conniving and manipulative, and takes advantage of Kenny's comparative naivete to steal his toys from him. At first, LJ confiscates the dinosaurs "one or two at a time", but one day, he hatches a plot to get a whole bunch of Kenny's dinosaurs for himself.
LJ suggests to Kenny that they should have "one great big battle" with the dinosaurs. Kenny's mother, afraid that Kenny will lose all of his toys to his unscrupulous "friend", has forbidden him to take out all of his dinosaurs at once, but LJ craftily convinces Kenny that they will need all of the dinosaurs for this particular game, and Kenny, caught up in the moment, thinks of a way to get more of his toys out of his room without his mother knowing. He runs upstairs and drops the pillowcase containing his dinosaurs out the window, and runs to get them before his mother is aware of what is going on. Kenny and LJ then stage a huge battle, with piles of dinosaurs getting blown up with pretend atom bombs.
At one point, LJ tells Kenny that the dead dinosaurs are radioactive, and must be buried to prevent the contamination from spreading. After they have hidden three piles of toys in the dirt, LJ distracts Kenny by suggesting that they go over to see "Banky and Larry Dunn's fort". Kenny gullibly agrees to the change of activity, and thinks he is being pretty wise by sneaking a peak at LJ's back pockets and socks to make sure he isn't taking any dinosaurs as they clean up. Unfortunately, Kenny has forgotten about the piles of buried "radioactive" dinosaurs, and when he realizes his oversight later that night and goes to look for them, he of course finds that LJ has gotten there first, and the dinosaurs are all gone (Chapter 3).
Kenny's toys get discarded in the dirt at Kenny's backyard when he plays with LJ. This is because LJ stole all of the dinosaurs when Kenny left to go do somethig else.