Parents need to know that violence here includes men killed by swords and arrows, a (briefly shown) crucifixion, and horses fallen in combat. A fiance plots murder against her husband-to-be, and there's a brief hint of royal incest. There's a conflict between Christianity and Islam (with a stalwart Christian-Catholic warrior as the hero), but a message that many Muslims are good guys, and Christians aren't necessarily honorable or correct.
Positive messages:Chivalrous warrior-knight Rodrigo practices mercy to enemies, chiefly the Moors (though some others he kills in single combat over honor), and also shows kindness to the helpless. He also remains faithful to an unworthy king on principle and gives up his personal happiness and his life for the greater good of his country. White actors in makeup generally portray Moors and north Africans.
Violence:Swordfights and jousting ending in fatalities. Men killed with knives and arrows. Brief depiction of a crucifixion. One man set on fire, another thrown off battlements.
Another issue on this great epic film is about its historicity and interest it may raise on actual events that portrays. Good movies based on real facts or people are valuable because they make people be interested on study that history's period, but parents should warn their kids do not take those films as documentaries.