Child stowaways, some as young as seven, were spilling off trains, after riding the rails from rural villages, and were about to disappear into the slums of India's capital, where they'd go to work picking garbage — or worse.
"My team in India says if we don't get to them in eight days, they're trafficked," recalled McCarney, the head of aid agency Plan Canada.
As World Refugee Day came and went on Wednesday, McCarney offered up the scene from a recent trip to help illustrate one of the most overlooked problems facing the world's displaced people: the uncontrolled and growing plight of undocumented, invisible children.
Many of the cherubs McCarney saw likely had no identity papers because they were likely never registered at birth.
It's a situation that is playing out across Asia, Africa and Latin America, and it is a situation acutely affecting children under the age of five.
Plan Canada, as part of the organization's international federation, launched its Universal Birth Registration campaign in 2005 to raise awareness, and tackle the problem.
Since then, they've helped register 40 million people in 32 countries, but that has been an uphill struggle because 51 million children a year are still not registered at birth.
As wars, famine and disaster force more people than ever to flee their countries, the United Nations refugee agency estimates that there are 12 million people who have been rendered stateless — with no provable citizenship connection to any country. It is believed that half of those — six million — are children.
The UN High Commissioner for Refugees singled out the problem of statelessness in its annual report this week on the world's growing refugee population, now pegged at 42.5 million.
But in doing so, the UNHCR acknowledged it does not have a firm grasp on the problem.
"Despite improvements in the number of countries reporting and in the reliability of reported figures, UNHCR was unable to provide comprehensive statistics on the number of all stateless persons in all countries around the world," it said.
Whether in their birth country or living as refugees, undocumented children are vulnerable to a wide range of exploitation, said McCarney, from being forced into becoming child soldiers, sex workers or cheap labourers in Third World factories and fields.
That deprives them of access to education or health services. It means tough times reuniting a child with their family if they do manage to flee an abusive situation.
McCarney, who has worked in more than 100 countries, can cite numerous examples. Two stand out.
In Ghana, for instance, cocoa industry bosses who were employing trafficked children couldn't be prosecuted because there was no way to prove the age of their young employees.
In northern Uganda, numerous children abducted and forced to fight with the rebel guerrillas, the Lord's Resistance Army, could not be reunited with their families.
"When children escape and they come back, they don't know who they are, so trying to reunite those children with their families and the communities — they don't remember," said McCarney. "They only had one identity."
The Canadian International Development Agency has helped fund birth registration programs as part of larger aid projects in Colombia and South Sudan, according to Plan.
Projects associated with Canada's G8 initiative on child and maternal health will likely provide other opportunities to help curb the rising numbers of unregistered children, said McCarney.
At the Canadian-hosted G8 summit in 2010, the Harper government created the Muskoka Initiative to help improve the health of poor children under the age of five and pregnant mothers in poor countries.
"There's a sharp focus coming out the Muskoka Initiative on newborns," she said.
"That's the wonderful opportunity to accelerate birth registrations and ensure that every child born gets an identity, and becomes official, and is counted."