If it's in the Bible, it took place. What I will say is that killing some infants in a small village doesn't rank up there in the minds of the contemporaries of that day...especially when you consider that the Romans crucified Spartacus' army and lined them for miles and miles on the Appian Way.
Lopez didnt start the Triple Alliance war by his lonesome
Argentina invaded Uruguay as I recall first and created a sympathetic state there
Brazil and Argentina were feeling their oats and Paraguay was worried and struck first in the Matto Grosso
A hot humid grassland and jungle area suited mostly for cattle
Anyhow Paraguay started with a nice army but was eventually decimated as you said from Brazil Argentina and Uruguay
It was foolish but Lopez was goaded and threatened
You can still feel the effects in Asunción