Researchers have warned that exposing children to TV shows that claim to improve speech might actually hinder speech.

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

Vocabulary gaining was put to test among 96 children who were 12 to 24 months of age by quizzing primary carers about development of children and exposure to educational media. Almost 50 per cent participants were handed over educational DVD to watch in their homes.

After six weeks when additional tests were conducted, no evidence was seen that could prove that watching DVDs actually helped them with their speech.

Infact, children who started watching infant DVDs at an early age scored lower on a test of vocabulary knowledge.