It started as an off-the-cuff question to Maria del Carmen Ferrez, who came to clean my house twice a month. Did she plan to have more children? Carmen, always chatty, suddenly went silent. She started sobbing. She told me about four children she had left behind in Guatemala. Her husband had left her, and Carmen simply couldn’t feed them more than once or twice a day. So she left them in Guatemala with their grandmother and came to work in El Norte. She hadn’t seen them in 12 years. Her youngest daughter was 1 year old when she left.

Carmen’s answer stunned me and sent me on a journey of my own. How could a mother leave her children and travel 2,000 miles away, not knowing when or if she would see them again? After nearly two years of research in the United States and in Latin America, I found some answers — and many more Carmens.

These mothers and children offer up almost certain proof that the legislative “solutions” that Congress is debating — and that brought thousands out into the streets in protest — can’t and won’t make a difference in the nation’s illegal immigration problem.

First, some facts. Immigrants’ low wages keep some businesses from closing or going abroad to compete. A 1997 study by the National Research Council, still considered the most objective and authoritative on the effects of immigration, found that immigrant labor lowered the cost of food and clothing for all of us, and it put such things as child-care services within reach of far more Americans than before.

And yet the downside is real, too. Because they have lower incomes, immigrants and their U.S.-born children qualify for and use more government services — including welfare — than the native-born. They have more children, and therefore more youngsters in public schools.

The cost-benefit calculation is just as troubling when it comes to the immigrants themselves. The mothers I talked to were able to send money to their children in their home countries so the kids could eat better and go to school past the third grade. But after spending years apart from their mothers, these children often felt abandoned, and they resented — even hated — their mothers for leaving them. Many mothers ultimately lose what is most important to them: the love of their children. Many children who found their way here later sought the love they hoped to find with their mothers elsewhere — in gangs, for example.

Will the proposals roiling Congress end the problems of illegal immigration? It’s not likely.

“Get tough” sums up one side in the debate, but it’s a policy that has had little success to date. The other, less draconian approach is to “control” immigration via temporary guest-worker programs and promises of future green cards — perhaps even citizenship.

Unfortunately, a past guest-worker program, in which Mexican braceros filled agricultural jobs between 1942 and 1964, laid the groundwork for the massive illegal migration of workers from Mexico that followed.

So what should the United States do? If you travel the routes that feed Latin Americans into the United States, you’ll come to believe that there is only one way to stem illegal immigration — at its source, in Mexico, Guatemala, Honduras and wherever people are desperately poor.

Instead of arguing about green card rules and wall heights, the United States should be formulating a new foreign policy. It should be aiming resources and diplomacy at improving conditions in Mexico and the few Central American countries whose migrants make up more than two-thirds of those in the United States illegally. Trade policies could give preference to goods from immigrant-sending countries to spur job growth. More aid could be invested there for the same purpose.

What I found out is that most immigrants would rather stay in their home countries with their extended families, with everything they know, than take the enormous risks required to cross the border and to make a new life here.