The only reaction I've ever seen my kids have to dead creatures is that they cry. DD1 regularly weeps over roadkill. She cries for ants that get stepped on, even if it's totally accidental. I even once totally broke DS's heart, by squashing a nasty silverfish I found in my bathroom. He still drags up the issue of the "nice crawly buggy dat mama mashed" and how much "him mama miss him" every once in a while. So no, I can't imagine them doing that. They've been raised with a very serious and almost exaggerated respect for life and death and I think it's sunk in.
That said-- I think I can imagine myself doing something like that, as a child. Certainly I can imagine some of the friends I had doing that. I don't think it means anything terrible or anything-- kids don't always stop and think, and are extremely curious about things. I would be upset by it, now, if I saw a child doing that, but I wouldn't read into it any terrible predictions about the child's future as a sociopathic mass murderer or anything....

Empathy and compassion are not fully developed in children, and they aren't supposed to be-- it's guidance, and our reaction to incidents like this, that teaches children to respect their fellow living things.