One in 25 children aged 10 or 11 'severely obese'
Height and weight measurements show the number of children classed as severely overweight rose from 15,000 in reception to 22,000 by the time they leave primary school.
The Local Government Association which analysed Public Health England figures said action was urgently needed.
The government insisted its childhood obesity plan was "comprehensive".
The weight and height of all children in England is measured when they start and leave primary school, under the government's national child measurement programme.
Figures from 2016-17 showed that for children in reception - aged four or five - about 1 in 40 (15,000 out of 629,000), was classed as severely obese
What you can do if your child is overweight.
- Lead by example.
- Encourage exercise.
- Eat healthily together as a family
- Limit Sugar
- Serve child-sized portions
You can check your child's BMI using the NHS's BMI calculator - you will need to know their height and weight.