A new study claims mothers-to-be who consume more fatty and sugary foods as they are "eating for two" could be putting their children at risk of obesity.
And the same may apply to mums who are breastfeeding, scientists said.
They found that unborn babies and newborn infants can have their eating habits programmed by their mothers' choice of food.
Children exposed to "junk food" in the womb or shortly after birth could find it hard to eat healthily as they grow older, the researchers added.
Writing in the British Journal of Nutrition, author Professor Neil Stickland said mothers should be better educated about the risks associated with poor diet.
He said: "The government is trying to encourage healthier eating habits in schools, but our research shows that healthy eating habits need to start during the foetal and suckling life of an individual.
"Giving children better school dinners is very good, but more needs to be done to raise awareness in pregnant and breastfeeding women as well.
"Future mothers should be aware that pregnancy and lactation are not the time to over-indulge on fatty-sugary treats on the misguided assumption that they are 'eating for two'."