She cited international studies saying parents should introduce solid food to their babies when they were 18 months old, and provide solid food in all meals by two.

The prevalence of drinking milk among babies was reflected in a 2010 study in which Chinese University, along with the Department of Health and Polytechnic University, interviewed parents of 1,588 children aged up to four.

They found 70 per cent of one-year-olds and 36 per cent of two-year-olds were drinking more than the recommended two cups, or 480ml, of milk a day, including fresh milk and formula.

Children who were fed on bottles tended to drink an average of 120ml more milk a day than those who used cups. Many international studies suggested an end to bottle feeding at 18 months old, Chan said, but the Hong Kong survey found 90 per cent of two-year-olds - and 55 per cent of four-year-olds - still using bottles.

More than half of the parents interviewed held the mistaken belief that follow-up formula - meant for slightly older children - contained nutrients that promoted brain development and could not be found in other foods.

Among parents of two-year-olds, 27 per cent thought milk should remain a major part of their diets.

'Some parents mistakenly think milk is the main food source for children, providing calcium that other foods cannot,' Dr Shirley Leung Sze-lee, the department's assistant director for family and elderly health services, said. 'We suspect this may be related to milk formula advertisements on television.'

The study also examined nine brands of formula milk and found their energy values were higher by a third than full-cream cow's milk.

Data from the department showed 5.7 per cent of children born in 2006 were obese at four, a rise from the 4.4 per cent of those born in 2002 to 2003. Leung said 20 to 40 per cent of obese children at that age would become obese adults.

55%

of four-year-olds were still drinking milk out of bottles

- 27% of parents see milk as a big part of a two-year-old's diet