It is an age-old battle with small children that most parents will recognise: please, please, eat your vegetables.

Some will read them books with titles such as The Boy Who Loved Broccoli. Others have been known to smother veg in tomato ketchup, or mix avocado and fruit with Greek yoghurt and call it icecream. Or resort to plain bribery.

Now, a study suggests there may be a more effective approach – but mothers need to start early.

Researchers have discovered that young children are less likely to react negatively to the smell of vegetables that they were repeatedly exposed to before birth.

The implications could be huge. Prof Nadja Reissland of Durham University, the study’s lead author, said a consequence would be “that you have a healthier population”.

Researchers gave some pregnant women kale powder capsules and others were given carrot powder capsules.

They then examined and coded the facial reactions of their child to carrot or kale. This was first done before the baby was born, using ultrasound, then repeated when they were about three weeks old. Most recently, 12 children were observed age three.

The images of a child exposed to carrots reacting positively to the smell of a cotton swab dipped in carrot and grimacing at the smell of kale speaks volumes.

The reaction of the children exposed to kale was similar – they were happy to smell kale but not carrot.

Reissland said the same patterns were repeated before birth, at three weeks and at three years.

“What we see over time is that the children are still more favourable to vegetables they were exposed to while they were in the womb. From this we can suggest that being exposed to a particular flavour in late pregnancy can result in long-lasting flavour or odour memory in children, potentially shaping their food preferences years after birth.”

Reissland said the team had alighted on giving carrot and kale powder capsules after some of the pregnant women balked at drinking so much kale juice or carrot juice in the name of science.

“Some of them said absolutely not. They were choking, couldn’t do it. I mean, it was all really good juice, very expensive.”

Reissland acknowledged that the research, funded by a grant from Aston University, in Birmingham, involved a small sample of mothers and children. “We really need to do a much bigger study and if we had the funding, we would.”

She said it would not cost much to give vegetable powder capsules to pregnant women in the hope of having a healthier population.

The idea could also be adapted to different cultures. “I’ve just come back from Japan … where you get loads and loads of fish. It is a different type of healthy eating, but if you get the foetus used to that food, then in later life they might be much more interested in eating healthily.”

The study included researchers at universities in France and the Netherlands as well as at Cambridge and Aston universities in the UK.

One co-author, Dr Beyza Ustun-Elayan of the University of Cambridge, said: “These findings open up new ways of thinking about early dietary interventions, suggesting that flavours from the maternal diet during pregnancy may quietly shape children’s responses to foods years later.”.

Another co-author, Dr Benoist Schaal from the CNRS (National Centre for Scientific Research), in France, said: “This study confirms that human foetuses can sense the flavours of foods that pregnant mothers eat, which might affect what they will like for years after birth. Research is needed on other odorants and how they affect the foetus and child.”

Reissland said there was still much to be learned about what affects the foetus, pointing to the presence of artificial sweeteners in so many products, including toothpaste.

The paper, Do Human Fetuses Form Long-Lasting Chemosensory Memories? is published in the journal Developmental Psychobiology.