NHS figures show it is the most common reason for children in England being admitted to hospital.
Some needed all 20 of their baby teeth removed.
The British Dental Health Foundation said some parents were not paying enough attention to the importance of their child's teeth.
Three years ago 22,574 children aged five to nine were admitted for rotting teeth, but provisional figures for the year beginning April 2013 show they have climbed to 25,812.
Figures from the Health and Social Care Information Centre show the next biggest cause of hospital admissions among the age group was tonsillitis, with 11,522.
"It is a case of child neglect," Nigel Carter, the chief executive of the British Dental Health Foundation, told the BBC.
"They're not giving the correct diet, they're getting sugary drinks. There's no attention to their oral hygiene regime and they're failing to take their children along to the dentist when their first teeth come through, and waiting until a child is in pain with a mouthful of rotten teeth."
Obesity and oral health
Fizzy sugar drinks, smoothies and fruit juices, already criticised as a cause of child obesity, are also being blamed.
Kathryn Harley, a paediatric dentist, said: "We see an awful lot in the media linking sugar to obesity and other health problems and not enough about the link between sugar in the diet and oral health."
Last month a group of scientists called for children to be given only water to drink to combat obesity and protect teeth.
Professor Susan Jebb, of the University of Oxford, said: "It comes back to simple advice to parents - encourage your children to drink water.
"Once they've been weaned, 'Children should be drinking water' is absolutely the message. Milk is fine, but that should be the mainstay of our advice."
In June, the Scientific Advisory Committee on Nutrition also called for people to more than halve their intake of added sugar.
It said sugar added to food or naturally present in fruit juice and honey should account for 5 per cent of energy intake.
But many people fail to meet the previous 10 per cent target.
One 330ml can of fizzy pop would take a typical adult up to the proposed 5 per cent daily allowance - and exceed a child's - without factoring in sugar from any other source.