Just a handful of questions:
1) Which parts of this R-rated horror film did you think they'd enjoy most? The scenes were people were slain graphically with machetes and arrows from a crossbow? The segment where a grizzled older man rolls off a bored student after grunting through sex, and she walks around with her shirt open for a while? Maybe the ones where people curse like drunken sailors who have just been mugged in an alley?
2) Could you really not afford a caretaker? I know they don't work for pizza any more, but was two hours' worth of babysitting beyond your budget?
3) I realize that, to some degree, your attendance was the distributor's fault: Lionsgate should have insisted that no one under 12 be admitted for any reason, and you should have been sent home or shunted over to another movie. But do you really think no harm was done by exposing your elementary schoolers -- the two kids I saw were little girls -- to savage images of slaughter?
4) Are you this neglectful and inept in all aspects of motherhood? If so, when your kids' moral fiber is as thin as a communion wafer someday, you may wonder how the heck they turned out so badly. The answer will be looking back at you from the mirror.