Almost three quarters of eight-month-old babies consume too much salt because they are fed too much processed food, cow's milk and bread, according to a report.
Tinned pasta and salty flavourings such as gravies and yeast extract are among the foodstuffs blamed by the University of Bristol researchers.
The nutritionists who carried out the study warned that high levels of salt consumed while very young can harm developing kidneys, give children a taste for salty foods and lead to poor habits that can persist into adult life.
High blood pressure established in childhood can track through to adulthood, the report says.
It adds that it is "extremely important" that parents receive clear and precise information over "appropriate foods" when they are weaning children.
Many parents are unaware of the amount of salt in manufactured foods and those of "low socioeconomic status" tend to be less well informed about "suitable" foods.
The research is part of a long-term ongoing study of parents and youngsters called Children of the 90s.
Though the raw research was done in the early 1990s, the authors say it remains relevant and they would expect the results to be similar if it was carried out now.
According to the research, most infants were first introduced to solids when between three and four months old.
The government's scientific advisory committee on nutrition advises that infants aged between seven and 12 months receive no more than 1g of salt a day.
The Bristol study found that 70% were receiving more than the recommended amount and some were consuming double the advised level.
Those consuming most salt tended to be taking cow's milk as a main drink – which is not recommended for children under a year – and to be eating bread.
Salty flavourings, canned pasta, yeast extract and baked beans also caused the researchers concern.
Pauline Emmett and Vicky Cribb, the nutritionists who conducted the research, said: "These findings show salt intakes need to be substantially reduced in children of this age group.
"Infants need foods specifically prepared for them without added salt, so it is important to adapt the family diet.
"This research suggests that clear advice is needed for parents about what foods are suitable for infants.
"This should be given to all parents and carers, and should include the important advice not to use cow's milk as a main drink before 12 months of age."
The researchers said progress had been made since the data was collected, with more manufacturers reducing the salt content of foods. But they said more needed to be done.
"Given that three quarters of salt in the diet comes from processed adult foods, successful salt-reduction strategies can only be achieved with the co-operation of the food industry.
"Manufacturers have a responsibility to reduce the salt content of food products. This process has already started in the UK but much more needs to be done.
"If this study were repeated today it is likely that there would be some improvement but not enough to safeguard the health of all babies."
The findings are being published by the European Journal of Clinical Nutrition.
