Many cultures through history have considered it perfectly acceptable to horribly murder men, women and children for essentially sport, as long as they were members of a hostile tribe. If you look at tribal cultures, you often find that the names in which a certain tribe refers to itself means something like "the people", "real people" or "true people". Members of foreign tribes, with no blood relations, alien customs and strange language, were often treated as effectively nonhumans in wartime - which is nicely documented and explained by human ethology btw. That is not to say that everybody had fun killing babies: but having fun doing it was certainly not ostracized as far as we can tell.
Even if we look at classical sources: Homer describes the murder of Hector's baby boy Astyanax during the sack of Troy without any impilcation of guilt, remorse, or breached taboos. Now, granted, killing Asytanax was necessary from a Greek standpoint, because he was the heir to the Trojan throne, but the way he was killed is so needlessly horrible, that it obviously requires a casually monstrous mind that goes way beyond simply eliminating the enemy: he is torn from her mothers breast by Neoptolemus, who then flings the infant over the wall of the city before his mothers eyes. Some versions of the story speak of Neoptolemus killing the baby in a different way, and then clubbing the king of troy to death with the corpse of his baby grandson. There is nothing in Greek mythology indicating such acts were considered grossly inappropriate, stigmatized or shameful. Neoptolemus is the son of Achilles, and a major hero.
That is not to say, that having fun killing the babies of your enemies was considered a moral imperative: but it is certainly not depicted as wrong either. It was just a thing nobody had serious problem with.