Urban warfare, as ancient Chinese philosopher Sun Tzu concluded, is the lowest form of warfare. The kind of fighting that coalition forces are likely to face in Baghdad involves complicated command-and-control challenges and presents soldiers and commanders with unparalleled tactical and ethical dilemmas. One such challenge is the Iraqis' use of children as urban guerrilla fighters.

The mobilization of children in armed conflicts and their transformation into killing machines is a worldwide phenomenon.

According to United Nations' estimates, there are more than 300,000 children participating in armed conflicts in places like India, Burma, Paraguay, Philippines and several African countries. In Sierra Leone alone, more than 5,000 children under the age of 18, both boys and girls and some as young as 6, are estimated to have fought in the conflict.

The last Western military to face the perils of children guerrillas was the Israeli army during Operation Defensive Shield in March-April 2002. In the Jenin refugee camp -- a cramped space inhabited by more than 15,000 people -- the Israelis became involved in fierce fighting with hundreds of militants. Many of them were children. Veterans of the battle reported that Palestinian children threatened them just like adult combatants and in some cases proved to be no less lethal than adults.

The Palestinian Islamic Jihad has recruited children as young as 13 for suicide missions. Others have been used to plant and detonate bombs.

American soldiers marching into Baghdad might face a similar challenge.

Iraq has one of the worst records of child participation in warfare.

Children under 18 years old make up about 50% of the country's population and are trained from a very young age to protect and defend the regime.

During the Iran-Iraq war, boys as young as 12 were part of the Iraqi military, and many of them died in suicide missions such as clearing minefields. Since the Gulf War, Saddam Hussein's regime has recruited thousands of Iraqi boys, teaching them to use small arms and brainwashing them with Baathist political indoctrination.

Hussein has also created child-soldier units -- Ashbal Saddam, or Saddam's Lion Cubs.

The Cubs -- the Iraqi equivalent of the Hitler Youth movement -- have trained about 8,000 young men in Baghdad alone who are considered to be well schooled in combat and ferocious.

The children units supply manpower to the Fedayeen Saddam, the paramilitary organization controlled by Hussein's son, Uday, likely to spearhead the Iraqi resistance campaign within Baghdad.

Child abuse is not limited to Hussein and his party. The Kurdistan Workers' Party, operating within Iraq, has been using an estimated 3,000 children, reported to be as young as 7, and like Hussein has created regiments specifically for children. Other armed opposition groups, such as the Patriotic Union of Kurdistan, have been known to use soldiers as young as 10.

Pictures of innocent-looking children killed by coalition soldiers are likely to resonate across the world, especially in those countries where opposition to the war is strong. The American public might also view such images with distaste, leading to weakened support for the war at home.

But those likely to face the toughest ethical and moral dilemma are allied men and women in uniform. Should they grant Hussein's Cubs immunity, or should they treat them like adults?

Most Western militaries still harbor cultural inhibitions about targeting children. Soldiers tend to get confused and hesitant when facing little men with guns, even when the rules of engagement allow them to use force against any enemy threatening them.

Deciding to pull the trigger on Saddam's Lion Cubs, whom they are likely to encounter, will probably be the most difficult thing this war requires them to do.