Hospital admissions for eating disorders have risen by more than a third (37%) across all age groups over the last two years, figures show.
Experts described the figures as "worrying" and urged the government to promote early intervention.
There were 19,040 admissions for eating disorders in 2018/19, up from 16,558 the year before and 13,885 in 2016/17.
The NHS Digital data for England found the most common age last year for patients with anorexia was 13 to 15.
A quarter of admissions in 2018/19 were for children aged 18 and under, at 4,471.
More than half of these (2,403) were for anorexia, up 12% from the previous year.
This included 10 cases of anorexia among boys and six among girls aged nine and under.
The data was acquired by the PA news agency.
In terms of older age groups in 2018/19, women aged 19 and over accounted for 5,274 admissions for anorexia and 3,542 for bulimia, while men accounted for 327 admissions for anorexia and 381 for bulimia.
Emma Thomas, chief executive of the charity Young Minds, said the figures were "worrying".
She added: "While there have been some improvements in community care for young people with eating disorders in recent years, it can still be difficult for children and young people to get the help they need before they reach crisis point.
"Getting early support for an eating disorder can prevent problems from escalating, meaning young people are more likely to fully recover.
"The government must make prevention and early intervention a priority for every child struggling with their mental health, to ensure that they get help as soon as they need it."
Dr Agnes Ayton, chairwoman of the faculty of eating disorders psychiatry at the Royal College of Psychiatrists, said healthcare staff "need to be better trained" at spotting eating disorders "as early diagnosis and treatment can reduce hospital admissions and saves lives".
Tom Quinn, director of external affairs at the eating disorders charity Beat, said there were a number of reasons to explain why there may be more young people being admitted to hospital.
"We know from our research and listening to the experiences of our supporters that it can often take a long while for early signs of an eating disorder to be spotted, for a referral to be made and for treatment to begin," he said.
"Therefore, while this rise in the number of young people admitted to hospital for treatment could mean that the number of young people with eating disorders is increasing, it could also be due to improvement in the ability of healthcare professionals to identify eating disorders."
Claire Murdoch, national mental health director for the NHS, said: "Waiting times for NHS eating disorder services are better than ever, with nearly 100 new or improved services in the community set up in recent years backed by millions in extra funding.
"It's clear that while the NHS is ramping up services through our Long Term Plan, the dangerous drivers of mental ill health need to be cracked down on by the rest of society."