Particular cultures channel when and how these traits are expressed, culture puts our nature through a lens, bending some elements and transposing others. The Romans had a culture where tenacious strength and indifference to suffering were such a fetish that it would be surprising if callousness and even cruelty were not commonplace, just as we would be surprised if veterans of a long and brutal war were not rendered somewhat less compassionate by the experience. The Nazis also tried to instill this hardness in their agents, with limited success, though the progress they made in such a short time can only indicate that they could have accomplished their goal in a generation or two. The cultural blink of an eye. Many boys seem to have a fascination with this sort of ruthlessness, I suppose because they need it.
Children can be stunningly cruel.
Then too people admire success, however achieved and children are less inhibited about it. For all but the most devoted members of a few pacifistic religions the moral question is not about bloodshed but about how and why. The modern view of a hero is a reluctant warrior. This view is a development of the moral outlook made popular by Christianity. Western governments and law operate on a principle of minimum force, though I think this is not so much a moral as a practical matter as the more intelligent student of history notes that brutality generates submission but also an atmosphere which is conducive of neither good economy or good governance.