Parents who refuse to help their obese children lose weight are neglectful, researchers have said.
While obesity alone is not a child protection issue, a "consistent failure to change lifestyle and engage with outside support indicates neglect", they 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," said experts writing online in the British Medical Journal (BMJ).
This involves parents who understand what is needed and are helped to get the right treatments for their child.
"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."
The team included Russell Viner, a reader in adolescent health at the Institute of Child Health in London.
They said poor parental behaviour was most worrying when the child was at risk of complications from their obesity, such as high blood pressure, Type 2 diabetes and difficulty with movement.
Failure to act should be regarded as a child protection issue when there is clear evidence of this behaviour "over a sustained period", they said.
And they added that "obesity may be part of wider concerns about neglect or emotional abuse".
This may include poor school attendance, exposure to or involvement in violence, neglect, poor hygiene, parental mental health problems or emotional and behavioural difficulties.