Parents who refuse to help their obese children lose weight are guilty of neglect, researchers have said.
The team, including Russell Viner of the Institute of Child Health in London, said obesity alone was not a child protection issue.
But a "consistent failure to change lifestyle and engage with outside support indicates neglect", it said.
Writing online in the British Medical Journal, it said actively rejecting help was a child protection issue.
The researchers said: "Childhood obesity becomes a child protection concern when parents behave in a way that actively promotes treatment failure in a child who is at serious risk from obesity.
"Parental behaviours of concern include consistently failing to attend appointments, refusing to engage with various professionals or with weight management initiatives, or actively subverting weight management initiatives."
They said such behaviour was of most worry when the child was at risk of obesity-related complications such as high blood pressure, Type 2 diabetes and difficulty with movement.
The team added that "obesity may be part of wider concerns about neglect or emotional abuse" such as poor school attendance, exposure to or involvement in violence, neglect, poor hygiene, parental mental health problems or emotional and behavioural difficulties.
However, they said parents were not always to blame.
"A consultation with a family with an obese child should not raise child protection concerns if obesity is the only cause for concern," they wrote.
"The outcomes of weight management programmes for childhood obesity are mixed at best, with the body mass index of some children falling substantially and that of others increasing despite high family commitment.
"As obesity remains extremely difficult for professionals to treat, it is untenable to criticise parents for failing to treat it successfully if they engage adequately with treatment."
The Royal College of Paediatrics and Child Health said obesity was primarily a public health problem not a child protection issue.
A spokesman said: "There may be a few families that give cause for concern where there are other matters of neglect or emotional harm and this is where paediatricians would have discussions with children's services."