A father answers the babbling happy-talk of his baby son while on line for lunch at McDonald’s one day in Washington, D.C.: “Shut up.” Born to a low station, the child suffers not only for lack of wealth but for a paucity of words. During the first several years of life, more affluent parents shower their children with millions more words, leaving poor kids with a “word gap” that may affect them for a lifetime.

In new research, Stanford University psychologist Anne Fernald says the word gap appears much earlier than previously thought — by 18 months of age, or so. By the age of 5, children from lower-income households may lag two years behind their counterparts in tests of language development.

According to Kimberly Noble of Columbia University Medical Center, brain imaging scans support the link between words spoken and brain development. Essentially, children of higher socioeconomic status use more of the brain’s “neural real estate” within regions involved in language development.

In this new study, Fernald says lower-income children reached a level of language proficiency richer kids had hit six months earlier. Children from higher-income families, by contrast, recognized more words and were better able to learn new ones from context.

In one experiment, the investigator placed voice recorders into the T-shirts of low-income toddlers from Spanish-speaking families, tracking the child’s language experience throughout the day. In listening to those recordings, a dramatic difference emerged in what scientists call “child-directed speech,” as opposed to words overheard merely from the background din of the television. Whereas one child in the study heard more than 12,000 word per day in such child-directed speech, another received only 670 words. Naturally, the language development gap between the two was significant.

"The advice I give mothers is to have conversations with your babies," Erika Hoff, a psychology professor at Florida Atlantic University, told CBS News. "Children can hear lots of talk that goes over their head in terms of the meaning, and they still benefit from it."

Yet, not all words are created equal, she advised. For some bilingual homes, for example, Hoff recommends the opposite of what you might think. She advises parents with broken English to refrain from mis-teaching their children America’s dominant language, but rather to focus on their native language — at least until they go to school.

Among tips for improved child language development, Fernald advises parents to begin speaking to their children in rich, complete sentences of varied structure, with no need for dumbed-down “baby talk.” In early language development, what matters most are child-directed words placing matters large and small — the universe and stuffed animals, for example — into context, she said.

The study findings were presented this month at the annual meeting of the American Association for the Advancement of Science.