Researchers surveyed the parents of 277 children and found that only a quarter recognised when their offspring were overweight. Where children were obese, a third of mothers and 57 per cent of fathers thought their sons and daughters were 'about right'.
The findings, published in tomorrow's issue of the British Medical Journal, underline the challenges facing food manufacturers, under pressure to offer healthier foods and try to stem the rise in chidhood obesity.
Some 30 per cent of British five-to-nine-year-olds are overweight or obese and this is expected to rise to 36 per cent by 2008, according to figures from Datamonitor. A recent report from the firm also suggests that there is evidence that parents are now placing greater importance on health as opposed to convenience when making purchase decisions.
Meanwhile food manufacturers appear to have cut advertising of the kind of sugary, 'junk' foods blamed for weight gain in children.
Yet the new survey by a team at the Peninsula Medical School in Plymouth, UK revealed that some parents showed a lack of concern towards their children's weight problems.
Although more than half of obese children's parents expressed some concern over their child's condition, only a quarter of parents of overweight children described themselves as even "a little worried" about it.
Misjudging weight problems was not confined to their children however. The researchers also found that of those parents who were overweight themselves, 40 per cent of mothers and 45 per cent of fathers judged their own weight to be "about right".
Contrary to previous findings, the study showed there were no differences between the highest and lowest socio-economic groups for the proportion of overweight parents, or for parents misjudging their children's weight.
"The longstanding inverse relationship between social class and obesity has been lost in the UK," say the authors, at the same time calling for change to the apparent lack of parental concern about overweight children.
"Until this is resolved we are missing critical partners in our efforts to stem an impending health crisis," they write.