The diets of all young children in Scotland deteriorated between the ages of two and five regardless of family income, a University of Edinburgh report found.
They found that perceived, rather than actual, changes in income were more likely to have an effect on the amount of unhealthy food a child eats.
Report author Dr Valeria Skafida, research fellow at the Centre for Population Health Sciences, said: "Changes in how parents felt about money were more strongly linked to their children's diets than incomes.
"This could be because income is not evenly distributed within the home, or because it is perception of poverty rather than measured poverty that determines food choices."
The study, which used data from the Growing Up In Scotland survey, compared the diets of around 3000 children at the ages of two and five and tracked the income of their parents.
It found that at the age of two 8.1% drank soft drinks more than once a day, rising to 28.7% by the age of five.
Some 6.4%never ate vegetables at the age of two, but this rate increased to 27.9% by the time they turned five.
Researchers concluded this may be because children become more able to demand and reject foods as they grew.
For parents whose financial situation changed from "feeling comfortable" to "finding it difficult" to cope, children ate fewer varieties of fruit and vegetables, and ate crisps and sweets more often.