Diego Martinez (l) and Hayley Ng. Photos via New York Daily News

Friends and relatives of the two children killed in Chinatown last week are grappling with what happened and why, as the parents of Diego Martinez and Hayley Ng demand that the driver whose carelessness led to their childrens’ deaths face consequences for his actions.

Over the weekend, companions of the fallen preschoolers contributed to a makeshift memorial on East Broadway between Market and Catherine Streets. Said the mother of a girl who considered Hayley her best friend: "We’re trying to sort it out. We’re trying to understand why it happened."

There is no single answer, as last Thursday’s catastrophe has revived fundamental questions of the responsibilities of drivers, traffic engineers, law enforcement personnel and legislators to keep people safe on city streets.

Meanwhile, reports the Daily News, two anguished mothers have questions of their own.

In a tearful reunion Saturday, Wana Wu and May Ng met for the first time since losing their children: Diego, 3, and Hayley, 4.

"Our children were killed and the driver walks away without even a ticket," said Ng, inside her sister’s Manhattan apartment. "How can this be? How can this be allowed?"

Sadly, Wu and Ng are not likely to be satisfied in their quest for justice. As Maureen McCormick, a Brooklyn assistant district attorney known for seeking tough penalties for drivers who kill, told Transportation Alternatives in a revealing 2004 interview, even aggressive prosecutors are often stymied by lax state laws and autocentric judges and juries. Said McCormick:

Because of the way laws are written and interpreted, and because of societal attitudes, it is easier to convict deadly drivers who are drunk or drugged. The average New Yorker has a hard time identifying with a guy who smokes crack or shoots up before getting behind the wheel. But jurors may identify with speeders or red light runners who kill someone.

The average New Yorker used to identify with drunk drivers, too, until a sweeping public awareness campaign made it socially unacceptable — except in Manhattan, where, thanks to DA Robert Morgenthau’s office, killer drivers under the influence still stand a good chance of catching a break.