Reese Martinich, nine months, bottom right, reaches out to Eileen Ladino as she leads a baby sign language class at a private residence on July 20 in Alexandria. (Matt McClain/The Washington Post)

The Alexandria living room reverberated with the babbling sounds of babies. “Babababababa,” 9-month-old Reese said to her mother, who offered an equally sincere “babababababa” in response. Avah sang out a happy “dadadadada” in between gumming a tropical-fish-shaped toy, and Liam cut through the din with a guttural “AAaaaaaaeeooooooohhhghhh!!!”

“You tell ’em,” said his father, James Johnson, 36, of Leesburg.

Many babies don’t graduate from jabbering to meaningful extended dialogue until they are closer to 2 years old. A growing number of parents, eager to communicate with their babies sooner, are starting conversations with their hands.

American Sign Language is increasingly becoming a temporary way to bridge baby talk and conversational English.

That’s why a dozen Northern Virginia parents gathered in a friend’s living room on a Saturday morning to learn signs for “ball,” “hat,” “milk” and “sunshine” from Eileen Ladino, a Gallaudet University -trained teacher who works with deaf and hard-of-hearing students in Fairfax County during the week and hearing parents and their pre-verbal babies on weekends.

Proponents say sign language promotes brain development and parent-infant bonding while giving babies a way to communicate their wants and needs a little earlier.

Starting at about 9 months, babies start using their hands and arms to communicate. They often learn to wave and clap and point, and their gestures increase as they begin to stand and walk, freeing their arms to move, said Brenda Seal, director of Gallaudet’s speech-language pa­thol­ogy program.

Babies can begin to imitate signs even if, as with babbling, they offer up a simpler version of the original.

Any kind of sign can come in handy, though, for parents desperate to understand the garbled demands of a frustrated toddler. (Oh, you want shoes! I thought you said juice!!)

“It was the fear of constant meltdowns that inspired me to do it,” said Christy Martinich, a new mom and wealth manager who hosted the class in her Alexandria living room this month.

Ladino told the group that babies can use signs to express more than basic needs. Long before she could string together sentences, Ladino’s daughter was making jokes, she said. At about 13 months, she smirked and signed “snakes” over a pile of spaghetti. Another time, she signed “bath” after dunking her Teddy Graham into a cup of water.

“One of the wonderful things about sign language is that you can peek into their minds and find out what they are thinking,” she said.

The growth of baby sign language is being fueled by a booming cottage industry of mostly mom-run businesses, with names such as Tiny Fingers and WeeHands, that offer lessons in yoga studios, living rooms and community centers.

Scores of books and hundreds of Web sites demonstrate signs suitable for baby mealtimes and bath time. Some teach American Sign Language, and some use other signs or gestures. More than 4 million viewers have clicked on the YouTube video “cute signing baby!,” which shows a 1-year-old in a highchair demonstrating dozens of signs at her mother’s prompting.

With some research to support their concerns, some parents worry that introducing signs or gestures competes for a baby’s attention and working memory and that it can potentially interfere with spoken-language learning.

But the most widely cited research shows the opposite to be true. A longitudinal study published in 2000 and funded by the National Institutes of Health showed that a group of babies who were exposed to signs or gestures along with talking scored better on multiple measures of language acquisition at 2 years old than children who were exposed to talking alone.

“When a baby learns to crawl, it doesn’t slow down [the process of] learning to walk. It gets them excited to move around,” said Linda Acredolo, a psychologist and retired professor from the University of California at Davis who was one of the authors of the study. “Signing makes babies excited about communicating.”

Her study showed that the early advantage started to level off by age 3. Nonetheless, the research has helped give rise to successful businesses and a broader movement.

Acredolo and another psychologist, Susan Goodwyn co-wrote the book “Baby Signs: How to Talk With Your Baby Before Your Baby Can Talk,” which has sold a half-million copies and is in its third edition. Their business also has trained 800 instructors in more than two dozen countries and worked with many preschools and day-care centers, including Early Head Start programs and child-development centers on many U.S. military bases.

Some say that successful studies of baby sign language do not reflect the power of signing but the extra efforts of parents who are highly motivated to engage their children in conversation.

“People who sign to their babies are people who are communicating to their babies and nurturing communication with their babies,” Seal said. “That’s the magic right there.”