More than four in 10 parents with underweight and overweight children mistakenly believe their children are in the average weight range, according to University of Melbourne research.
The study also finds that different methods of assessing children's weight - such as BMI or waist circumference - result in different rates of children being identified as overweight or underweight. According to BMI, more children were classified as overweight, than compared to waist circumference.
The study, by doctoral researcher Dr Pene Schmidt, also finds that children who are not in the average weight range, are also more likely to over or underestimate their body size.
It also finds a small number of parents believe their underweight children are overweight or that their overweight children are underweight.
Dr Schmidt says the research points to a need to overhaul the ways in which children's weight is classified and provide better information to parents about appropriate weight at both ends of the spectrum.
"Parents are unlikely to take the necessary preventative actions if the perception of their child's weight - whether underweight or overweight - is incorrect,'' she says.
Dr Schmidt, who completed her study in the University of Melbourne's School of Behavioural Science, analysed data from a survey of more than 2100 Victorian children and their parents aged from 4-12.
While previous research has examined parental perceptions of overweight children, Dr Schmidt's study is believed to be the first to also examine attitudes toward underweight children using both BMI and WC.
Dr Schmidt compared objective measures of children's weight - such as Body Mass Index and waist circumference - with subjective perceptions of whether parents and children thought they were overweight, average weight or underweight.
She found that:
- More than 4 out of 10 (43 per cent) parents of underweight children were incorrectly considered to be average weight by their parents;
- Almost half (49 per cent) of parents of overweight children incorrectly believed their child was average weight;
- More than 8 out of 10 parents correctly identified average weight children as being average weight;
- A very small percentage of parents assessed underweight children as being overweight (1.4 per cent) and overweight children as being overweight (2.5 per cent)
- Parents were more likely to report that their sons were underweight and that their girls were overweight.
- Parents were less likely to accurately identify that their child was underweight.
- Parents of boys were less likely to accurately identify their child as being overweight.
- Twice as many parents expressed concern about their child being overweight compared to underweight.
- Only 4/10 underweight girls and half of underweight boys correctly assessed their weight.
Dr Schmidt said the study showed that parents and children were struggling to determine whether they were the correct weight.
She said this showed there needed to be more research to determine how to best define children's weight status - and how to communicate this to children and parents.
"This study also suggests a strong social bias among both parents and children towards thinness,'' she said.
"While public health campaigns are directed towards the prevention of obesity, it's also important that the messages are getting through to the right groups."
"In particular we need to make sure that the focus on reducing the number of overweight children does not have the adverse impact of increasing the number of underweight children."
Dr Schmidt was recently conferred with a Doctor of Psychology at the University of Melbourne. She works clinically in the field of eating and weight related disorders.