Many parents think they're helping their baby's language by letting them watch a Baby Einstein DVD, but the opposite might be the case, according to a study out Tuesday.

The study found that with every hour per day spent viewing baby DVDs and videos, infants between the ages of eight and 16 months learned about 10 per cent fewer new vocabulary words compared to babies who never watched the targeted programming.

As well, the study showed that babies in the same age range who watched other types of programming such as children's educational shows, children's non-educational shows, kids movies or adult television learned more words, versus babies watching infant-geared shows.

For toddlers aged 17 to 24 months, the article found that baby DVDs and videos had neither a positive nor a negative effect. 

The paper was published online Wednesday in the Journal of Pediatrics. It was done by researchers at the University of Washington and Seattle Children's Hospital Research Institute who quizzed 1,008 Minnesota and Washington parents about their babies' viewing habits. They also completed a standard evaluation for measuring infant language development.

"Despite marketing claims, parents who want to give their infants a boost in learning language probably should limit the amount of time they expose their children to DVDs and videos such as Baby Einstein and Brainy Baby," said a statement about the study.

'Babies learn their language best from a person, not a TV or a video.'—Study co-author Andrew Meltzoff

One of the study's co-authors, Andrew Meltzoff, co-director of the University of Washington's Institute for Learning and Brain Sciences, told CBC News that, "The study shows that parents are the baby’s best teacher and that babies like people, people, people. Babies learn their language best from a person, not a TV or a video. They learn language and the ways of the culture from watching us. We are role models for our children.

"Parents and caretakers are the baby’s first and best teachers. They instinctively adjust their speech, eye gaze and social signals to support language acquisition. Watching attention-getting DVDs and TV may not be an even swap for warm social human interaction at this very young age. Old kids may be different, but the youngest babies seem to learn language best from people," said Meltzoff in a release. 

One of the study's other authors, Dr. Dimitri Christakis, a pediatrics researcher at Seattle Children’s Hospital Research Institute and a University of Washington pediatrics professor, said, "In my clinical practice, I am frequently asked by parents what the value of these products is. The evidence is mounting that they are of no value and may in fact be harmful.

"Given what we now know, I believe the onus is on the manufacturers to prove their claims that watching these programs can positively impact children’s cognitive development," he added.

The paper is part of a bigger project examining media content in the first two years of life, and the effects of content on young children. Last spring, the researchers found that by three months of age, 40 per cent of babies are regular TV watchers, with that number jumping to 90 per cent by two years of age.