Parents who buy educational DVDs to give their toddlers a head start may be doing more harm than good. A study of almost 100 boys and girls aged between one and two found that regularly watching a DVD from the Baby Einstein range did nothing to boost their vocabulary.

In fact, the younger the children were when they began to watch the programmes, the worse their word power. Researchers tested the children over six weeks. Half were given a Baby Wordsworth DVD, which their parents were told to play 15 times over six weeks.

The 35-minute disc, costing around £18, is part of the Baby Einstein range - popular with parents keen to boost toddlers' IQs before starting school. It uses puppets and people to introduce 30 words for rooms and household appliances, including 'fridge' and 'phone'.

The remaining children's parents were told to 'go about life as normal'. Not surprisingly, older children picked up more new words than younger ones, the California University team found. However, those who watched the DVD did no better than the others, and in fact appeared to learn little or nothing, their parents told Archives of Pediatrics & Adolescent Medicine, an American journal.

Researchers also asked parents if they had used the DVDs before and found the younger a child was on starting to watch Baby Einstein, the worse their word ability was. This may be because parents are more likely to use them as aids if children are struggling to learn to speak, said researcher Rebekah Richert.

It is also possible that watching TV means youngsters miss out on playing with their parents, other children and toys. In addition, some experts say the flashing lights and quick scene changes in the Baby Einstein programmes over-simulate the developing brain.

Dr Richert said: 'Given that infantdirected media are nearly ubiquitous aspects of many infants' lives, research should continue to examine whether and how parents can use the DVDs effectively.'

Last night, no one at Disney was available for comment. The Baby Einstein DVDs avoid any suggestion they will make children brainier, and merely claim the series is a must for parents who simply want the best for their children.

'Our products provide fun and stimulating ways for parents and carers to interact with their children,' the blurb on the DVD says.

A previous study found children between seven and 16 months who watched the DVDs knew fewer words than their peers. Each hour they watched per day equated to six fewer words in their vocabulary.

Following threatened legal action last year, Disney offered refunds to dissatisfied parents - but only in North America.