Experts suggest parents use long sentences when having a conversation with children. [Photo provided to China Daily]

Stanford's Fernald discovered this when she compared how children mentally process the language they hear. Lower-income children in her study achieved at age 2 the level of proficiency that more affluent kids had reached six months earlier.

To understand why language processing is so important, consider this sentence: "The kitty's on the bench." If the youngster knows the word "kitty", and his brain recognizes it quickly enough, then he can figure out what "bench" means by the context. But if he's slow to recognize "kitty", then "bench" flies by before he has a chance to learn it.

Next, Fernald tucked recorders into T-shirts of low-income toddlers in Spanish-speaking households to determine what they heard all day - and found remarkable differences in what's called child-directed speech. That's when children are spoken to directly, in contrast to television or conversations they overhear.

One child heard more than 12,000 words of child-directed speech in a day, while another heard a mere 670 words, she found. The youngsters who received more child-directed speech processed language more efficiently and learned words more quickly, she reported.

But it's not just quantity of speech that matters - it's quality, Hoff cautions. She studied bilingual families and found that whatever the language, children fare better when they learn it from a native speaker. In other words, if Mom and Dad speak Spanish but aren't fluent in English, it's better for the child to have a solid grounding in Spanish at home and then learn English later in school.

Next, scientists are testing whether programs that teach parents better ways to talk to tots really do any good. Fernald says preliminary results from one of the first - a program called Habla Conmigo, Spanish for Talk With Me, that enrolls low-income, Spanish-speaking mothers in California in the US - are promising.

Fernald analyzed the first 32 families of the 120 the program will enroll. Mothers who underwent the eight-week training are talking more with their toddlers, using higher-quality language, than a control group of parents - and by their second birthday, the children have bigger vocabularies and process language faster, she says.

Associated Press