By Branwen Jeffreys
Health correspondent, BBC News
Doctors say they are now seeing children as young as six months old in their obesity clinics.
Portion sizes should be appropriate for age
They are concerned some parents are supersizing meal portions for very young children and have lost sight of what "normal" weight looks like.
They told the BBC that in extreme cases overfeeding a young child should be seen as a form of abuse or neglect.
A BBC investigation has learned obesity has been a factor in at least 20 child protection cases in the last year.
The BBC contacted almost 50 consultant paediatricians around the UK to ask if they believe childhood obesity can ever be a child protection issue.
Dr Tabitha Randell, a consultant paediatrician from Nottingham, is one doctor who believes some parents are killing their children with kindness.
In one extreme case Dr Randell saw a child aged two-and-a-half who weighed more than four stone (25.4 kg). Children of this age should weigh around two stone.
"They said she was big-boned and they were too. I think the perception of parents is a very real problem.
"If you see every other child in the playground with their belly hanging over their trousers you think that's normal."
In virtually all of the cases, it is down to overfeeding, according to the doctors surveyed.
PORTION SIZES FOR ONE YEAR OLDS
One tablespoon of finely chopped meat or fish or one egg, 2-4 times a day
Half a small apple, pear or one small plum, 2-4 times a day
One tablespoon of vegetables, 3-5 times a day
One slice of bread or one tablespoon of potato, rice or cereal, 4-6 times a day
Avoid foods high in fat or sugar
The were concerned that some parents no longer understand the correct portion sizes for very young children or select the wrong types of food - crisps, fizzy drinks and other sugary or high fat snacks - for their child.
One of the doctors said they knew of a parent who had fed a baby a McDonald's milkshake with a bottle and a teat.
But some health professionals think it is unhelpful to see childhood obesity as potential neglect.
The Royal College of Paediatrics and Child Health said: "Obesity is a public health problem, not a child protection issue."
Some parents feel they face an uphill struggle to convince their children to eat healthily in a society where there are many high fat choices on offer.
PORTION SIZES FOR 2-3 YEAR OLDS
One and a half tablespoons of fish or meat, 2-4 times a day
One small apple, pear or banana, 2-4 times a day
Two tablespoons of vegetables or one small salad, 3-5 times a day
One large slice of bread or up to two tablespoons of cereal, rice or potato, 4-6 times a day
Four small cubes of cheese or three tablespoons of yoghurt, 2-4 times a day
500ml of full fat milk in a day
Limit fatty or sugary food - six small chips or one biscuit or small slice of cake
Three glasses of milk
At the children's centre in the deprived Meadows area of Nottingham parents are offered support to improve their children's diet.
A group of mothers has just signed up for a six-week course, learning how to prepare healthy food from scratch.
The mothers say it is too easy to blame parents.
Vikki Sansom, who has two young children, said: "I think there is a big difference between not feeding and overfeeding.
"It's really hard for parents and it's wrong to say that's neglect".
The British Medical Association is due to debate a motion on this issue at its annual conference at the end of June.