In fact, parents interviewed between 2005 and 2010 were 24 percent less likely to spot a weight problem in their child than parents interviewed between 1988 and 1994, the researchers said.
The report was published Aug. 25 in the online journal Pediatrics.
"The society as a whole is stuck with a vicious cycle," said senior study author Dr. Jian Zhang, an associate professor of epidemiology at Georgia Southern University in Statesboro.
"Parents incorrectly believe their kids are healthy, they are less likely to take action, and so it increases the likelihood that their kids will become even less healthy."
Obesity has more than doubled among children aged 6 to 11, rising from 7 percent in 1980 to nearly 18 percent in 2012, researchers said in background information.
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Pediatricians will be key to breaking the cycle, said Amanda Staiano, director of the Pediatric Obesity and Health Behavior Laboratory at the Pennington Biomedical Research Center in Baton Rouge, La.
"Parents see doctors as an authority figure, and we see success with weight loss interventions and treatments when a pediatrician is involved," said Staiano, who also serves as co-chair of The Obesity Society's Public Affairs Committee.
"It's paramount that every time a child comes in for a visit, the pediatrician reviews the child's height and weight, and discusses how they are doing with their parents."
The new study relies on data gathered during the U.S. National Health and Nutrition Examination Survey, which has been conducted at regular intervals by the U.S. Centers for Disease Control and Prevention since the early 1960s.
In the survey, parents of children aged 6 to 11 are asked whether they considered their child to be overweight, underweight or just about the right weight. CDC technicians then measure the child's weight and height, and use those to calculate their body-mass index (BMI).
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Parents surveyed between 1988 and 1994 correctly perceived about 51 percent of the time that their child was overweight or obese. That number slipped to 44 percent for parents asked to assess their child's weight status between 2005 and 2010.
More than three-quarters of parents interviewed in the 2005-2010 survey perceived their overweight children as "about the right weight"; 83 percent for boys and 78 percent for girls, researchers report.
The advent of the childhood obesity crisis likely has made it more difficult for parents to perceive that their child has gained a potentially unhealthy amount of weight.
"We compare ourselves to the people we see around us. If a child is in a class where most of the kids are overweight or obese, that becomes the new normal," Staiano said.
In addition, medical definitions of obesity and overweight have become overly complicated, so much so that parents may have a hard time accurately applying the standard to their child, Zhang said.
"The recommendation developed by the CDC is fairly complicated, and it can be very hard for parents to understand that," he said.
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Both Zhang and Staiano said parents also could be influenced by the stigmatization of obesity, and are reluctant to label their child as overweight or obese for fear the kid will suffer hurt feelings or face cruel taunts from others.
"Nowadays, parents may be concerned there is a stigma if they admit their child is obese. They also may not know what to do about it, so there may be a little bit of denial there as well," Staiano said.
Zhang agreed with Staiano that pediatricians are likely the only people who can effectively intercede.
"Practitioners are in an ideal position to help the parents and correct their misperception. Without help from professionals, the epidemic of childhood obesity cannot be reversed," Zhang concluded.
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