The government is launching a plan to tackle obesity by helping parents recognise the warning signs that their children are overweight.
Parents need more support to encourage healthy eating
It follows a claim by the Medical Research Council that many people do not know their children are overweight.
The Department of Health has pledged to do more in the next year to support parents in encouraging healthy eating and physical activity.
But critics said the government had not acted quickly enough to tackle obesity.
The government has set a target of halting the yearly rise in rates of obesity in the under-11s by 2010.
But Dr Susan Jebb and colleagues from the Human Nutrition Research unit at the MRC found several major barriers were preventing families from adopting healthy lifestyles even though they knew the importance of a healthy diet and exercise.
Their review of the evidence showed people have a poor perception of their own weight status and are even worse at spotting when their child is overweight or obese.
Busy lifestyles, irregular working hours and fears that having a healthy lifestyle is too difficult to achieve also put people off healthy choices.
According to the MRC report, average time spent preparing meals has fallen from two hours to just 20 minutes over the past two decades.
And safety concerns prevent children being allowed to walk to school or play outside.
One of the biggest problems facing parents is their child's willingness to accept new foods.
Trying to coax children to eat healthily often takes a backseat to trying to have a pleasant mealtime, said the researchers.
Dr Jebb said 80% of parents recognised that an unhealthy diet and lack of physical activity contributed to obesity.
"But people don't necessarily realise that it applies to their child," she said.
"More than 40% of children over the age of six choose their evening meal on half of all occasions but they lack the skills to choose wisely.
"It's not surprising that parents try to avoid conflict to make a pleasant atmosphere at home but it leads to a lack of exposure and familiarity with different foods."
Launching the Government's Healthy Living Programme, Public Health Minister Caroline Flint said they would be rolling out a series of initiatives to support families, such as 'Top Tips for Top Mums' to help families share ideas for getting children to eat fruit and vegetables.
"We're not short of information but the information hasn't always been leading to behaviour change," she said.
"This is where the theory becomes reality - something that is really meaningful for people."
Andrew Murrison, the shadow health minister, said: "There is no question that the government has not done enough and what they have done has not been done quickly enough.
"When it comes to implementation they have failed so far."
Dr David Haslam, clinical director of the National Obesity Forum, said obesity had been a priority for the government but nothing to date had made the slightest bit of difference because of a lack of concrete ideas.
"At least they're putting measures in place to try and actively do something," he added.