My 10- and 12-year-old sons are immersed in this sea of dissonance, hearing about a terrible new war and worried that they will have to fight it. At their Roman Catholic school in Chicago, they join their classmates in heartfelt prayers for peace. Then they come home to watch President George W. Bush explain the need to drop bombs on Taliban targets. Squaring entreaties to God with the horrors of warfare is a treacherous minefield for parents: this sounds suspiciously like the same fanatical rationale that religious extremists cheerfully embrace.

So my wife and I have searched for ways to differentiate. Conjuring up playground bullies has worked well; I’ve had no argument from our sons when I suggest that defending oneself from the class bully is much different than picking a fight. And applying that moral template to Osama bin Laden is distressingly easy. He has essentially claimed credit for the terror attacks–and promised to launch more. He is, as Americans have been reminding one another, a proven killer who wants us all dead. I’ve also had some luck plagiarizing the always-serviceable Florentine statesman Niccolo Machiavelli, who back in 1513 advised that if war is inevitable, delaying it only helps one’s opponents.

But these are anecdotal arguments, unconnected dots. Kids respond better to thoughts that have some overall architecture. So I’ve reached even deeper into the pile of centuries to steal guidance from the likes of Saint Augustine and Saint Thomas Aquinas. Armed with my kid-friendly version of their criteria for a just war, I’m inverting the antiwar arguments that, 30 years ago, my generation wielded to extract the United States from the quagmire of Vietnam (and, less nobly, to avoid the military draft).

This time, I’m out to show that even a bloody campaign against terrorists can be not only justified, but is an obligation that Americans can’t, in good conscience, ignore. With the ghosts of Augustine and Aquinas looking on–I imagine them hovering, approvingly, over the refrigerator–I explain to my sons that the necessary conditions have been met: the September 11 attacks followed years of U.S. restraint after the bombings of our embassies and other targets; the murders of some 5,000 people beg for justice and self-defense; yes, regrettably, civilians will be killed in this war, but its long-term benefits outweigh its costs. For good measure, I toss in something the A saints didn’t think to mention: with more terror attacks promised, we have no choice but to respond.

The fact that other countries have joined in this military effort is a big help. Children understand the notion of partnerships, like the ones that cost Americans oceans of blood in two world wars. Any nation willing to put young lives on the line, as Britain, France, Australia and others are doing, proves that some bonds defy self-interest and cynicism. Those governments are resisting the myopic perspective of Charles de Gaulle, who in 1966 loftily demanded that the United States remove its soldiers from France. U.S. Secretary of State Dean Rusk’s trenchant retort: “Does that include the dead Americans in military cemeteries as well?”

All of this history and reasoning is more than I can expect my kids to absorb. And yet it is far less than what children who lost parents on September 11 must absorb. Yes, my kids have their fears. But because hundreds of miles separate them from the East Coast epicenters, they aren’t as afflicted as the New York schoolgirl who, according to one newspaper account, recently wondered aloud in class whether candy can contain a bomb.

I’m not the only American who is infuriated that such thoughts now obsess victimized children–or the only one who realizes that too many kids in too many countries live every day amid far more realistic dangers. There is a new sense here that, as the terrorist threat eventually subsides, Americans must help find ways to reduce the perils those children face.

Back at my own kitchen table, I finally have some assurances, however limited, for my sons. I can tell my 12-year-old that many people share his determination to protect Chicago and everywhere else terrorists might strike. And I can tell my 10-year-old that, because of some courageous soldiers from several lands, I believe this war will end before he is, in fact, old enough to fight it.