Researchers have warned that early exposure to shows that boast they can improve speech; could actually hinder their speech development.

Children aged between one and two who are exposed to instructional programs and DVDs, claiming that they help in improving speech, do not necessarily improve their vocabulary. Infact, they do not have any effect on their learning.

"Parents who are concerned about their children's poor language abilities may use baby DVDs to try to teach their children", says Dr. Rebekah Richert from University of California.

"Parents who use baby DVDs early may be less likely to engage in behaviours that promote language development or early viewing of baby DVDs may actually impair language development".

It was found in the study that although the infants were exposed to up to two hours of viewing per day from five months old, program makers' claims could not be "substantiated".

The vocabulary acquisition was examined among 96 children, aged 12 to 24 months, testing the infants on measures of vocabulary and general development.

Dr. Richert said, "We found that over the course of six weeks, the children watching the DVDs didn't learn any more words than children not watching".