Even CNN admits that the Aztecs deserved the wrath of Cortez:
Aztecs butchered, ate invaders. This grisly story is from today's online edition of CNN. Domestic nations have tried many tactics over the ages to repel invading armies. The Aztecs were no different and a recent find indicates they even resorted to sacrificing and eating hundreds of people in 1520.
The article notes, "Skulls and bones from the Tecuaque archeological site near Mexico City show about 550 victims had their hearts ripped out by Aztec priests in ritual offerings, and were dismembered or had their bones boiled or scraped clean, experts say."
Most of the victims were not Spanish soldiers. The were part of a large party that was made up mostly of the mulatto, mestizo, Maya Indian and Caribbean men and women given to the Spanish as carriers and cooks. As such, it was a slow moving group and proved an easy target to the Aztecs who were normally unable to defeat the Spanish in battle.
CNN Link (nasty details in the article--be sure to read them to your four-year-old daughter, then explain how all cultures are equal).