Most parents are feeding their babies solid foods too early - raising their risk of obesity and diabetes, according to new research.
More than half of infants are being started on them before the recommended six months of age - with one-in-six beginning before they are even four months old.
On the other hand one-in-eight don't commence until they are at least seven months old - with only a third being introduced at the right time.
The study of almost 1,500 babies across the US - the first of its kind - emphasises the need for them to be given solid - or 'complementary' - foods at the proper time, say health experts.
Previous research has suggested doing it prematurely can make babies more prone to developing chronic diseases such as diabetes and coeliac disease later in life - as well as piling on the pounds.
Dr Chloe Barrera, a nutritionist at the Centres for Disease Control and Prevention (CDC) in the US, said: "Introducing babies to complementary foods too early can cause them to miss out on important nutrients that come from breast milk and infant formula.
"Conversely, introducing them to complementary foods too late has been associated with micronutrient deficiencies, allergies and poorer diets later in life."
The study, published in the Journal of the Academy of Nutrition and Dietetics, found babies who were never breastfed or breastfed for less than four months were most likely to be given the foods too soon.
Current guidance stipulates infants should be introduced at around six months.
So Dr Barrera and colleagues analysed six years of data from the uniquely detailed National Health and Nutrition Examination Survey (NHANES) - a study carried out by the CDC.
This allowed them to assess the food intake of 1,482 children aged six to 36 months gathered during household interviews with parents or other guardians.
The survey asked how old infants were when they were first fed anything other than breast milk or formula.
This includes juice, cow's milk, sugar water, baby food, or anything else that the infant might have been given - even water.
It found only 32.5 per cent were introduced to complementary foods at the recommended time.
One-in-six (16.3 per cent) were started before four months, almost four-in-ten (38.3 per cent) at four to five months and one-in-eight (12.9 per cent) at seven or more months.
The researchers say their findings help understand the current state of infant feeding practices in the US.
Over the last 60 years recommendations for when to introduce solid foods have changed dramatically.
The 1958 guidelines suggested solid foods in the third month, the 1970s brought a delay until after four months and the 1990s pushed the introduction out to six months.
These changes have influenced many past studies of infant nutrition most of which show a general lack of adherence to current professional guidelines - whatever they may be.
The US Department of Agriculture (USDA) and Department of Health and Human Services (HHS) are currently developing the first federal dietary guidelines for children under two years, to be released in 2020.
Dr Barrera said: "Efforts to support caregivers, families and healthcare providers may be needed to ensure US children are achieving recommendations on the timing of food introduction.
"Inclusion of children under two in the 2020-2025 Dietary Guidelines for Americans may promote consistent messaging of when children should be introduced to complementary foods."
Human milk provides all the nutrients - including iron - that babies need for about the first six months of life.
But once the iron stored during pregnancy is used up - at about 6 months of age - iron-rich foods such as meats or iron-fortified cereals need to be added to the baby's diet.
Plus, most babies are developmentally ready for solid foods around 6 months of age.
Signs that your baby is ready for solid foods include the ability to sit up with little support, the ability to hold its head up, the development of motor skills to pick up soft foods and the ability to put them in its mouth.
But the controversy surrounding the introduction of solid foods continues unabated.
Parent surveys of more than 12,000 children at the age of 9 months, 3 years and 5 years - as part of the UK-wide Millennium Cohort Study - prompted the recommendation that solid foods be introduced no sooner than 4 months of age.
They found that when solids were introduced before 4 months, children (26 percent) were more likely to be overweight or obese at 3 and 5 years of age compared to babies given solid foods after 4 months of age (22 percent).
Researchers also concluded that children who were not breastfed were more likely to become overweight (23 per cent) compared with those breastfed for at least until four months old (18 per cent).