A government association representing more than 400 councils in England and Wales said parents of dangerously obese children are at risk of losing them.
The Local Government Association warned that the worst cases of obesity will be increasingly seen as evidence of "parental neglect," and that social workers will have to step in to offer advice to protect the child's welfare.
In the most extreme cases, children could be taken away from parents.
The stark message came as town hall bosses revealed the impact of fat Britain:
— Councils are fitting super-size cremation furnaces to cope with fat corpses
— Ambulances have fitted extra-wide stretchers and winches for obese patients
— Schools are buying bigger seats for classrooms
About 1 in 4 people in England is obese and considered so overweight that it threatens the person's health.
LGA public health spokesman David Rogers said some councils are already taking actions "where parents are putting children's health in real danger.
"Councils would step in to deal with an under-nourished and neglected child so should a case with a morbidly obese child be different?" he continued. "There needs to be a national debate about the extent to which it is acceptable for local authorities to take action in cases where the welfare of children is in real jeopardy."
Sixteen percent of American children are overweight or obese, according to the Centers for Disease Control and Prevention.
Efforts have been made in the U.S. to reduce children's access to fast food, soda and snacks, especially in public schools. Fitness guru Richard Simmons recently called on Congress to expand gym class offerings in schools. And the city of Los Angeles last month put a moratorium on new fast food restaurants in South Los Angeles, where childhood obesity has reached epidemic proportions.