Children who increase the number of hours of weekly television they watch between the ages of two and four years old risk larger waistlines by age 10.
A Canadian study found that every extra weekly hour watched could add half a millimetre to their waist circumference and reduce muscle fitness.
The study, in a BioMed Central journal, tracked the TV habits of 1,314 children.
Experts say children should not watch more than two hours of TV a day.
Researchers found that the average amount of television watched by the children at the start of the study was 8.8 hours a week.
This increased on average by six hours over the next two years to reach 14.8 hours a week by the age of four-and-a-half.
Fifteen per cent of the children in the study were watching more than 18 hours per week by that age, according to their parents.
The study said the effect of 18 hours of television at 4.5 years of age would by the age of 10 result in an extra 7.6mm of waist because of the child's TV habit.
Source: BBC News