I think there's so much more to it than parents being uneducated about healthy eating, although that is definitely a part of it. IMO in alot of cases, overeating is a symptom of an emotional problem too. Many overweight people use food as a comfort, or a crutch, and teach their DC by example.
I think if overweight people want the help, it should be offered alongside counselling, and with encouragement and support, not accusations of how poor their parenting skills are.
I have a friend who is stick thin, but her DD is 5'0 and 18 st. In this case, my friend was v. v. hungry as a child, and was given v. v. small portions, so she was always hungry, even straight after eating. This left my friend with a deep seated fear of her DD ever being hungry, so she overcompensated, preparing lavish meals of whatever her DD desired every time her DD uttered the words 'I'm hungry'. This friend is happy to cook a substantial meal at 10pm if her DD complains she is hungry, and this is all down to her fear that her DD will feel the way she did as a child. As a result, and because DD is pretty much left to her own devices ignored, apart from when she is having food prepared for her, DD has grown up to associate food with receiving love and attention, so it's become an emotional problem.
Even my HV told me that she finds alot of mothers from when their DC are born, will feed their babies whenever they cry, even if the baby has just been fed, and the babies grow to associate love and attention with food, because the parents don't know what else to do when their babies cry, these parents quite often go on to reward their children with food treats, instead of any other treats, and the cycle goes on.
So partly down to education, but it's not as easy as just re educating parents, it's supporting them through the reasons why they overeat and overfeed their children in the first place IMO.