They say advances of the past 40 years are being reversed by poor diets and a lack of care.
Many kids are getting cavities early, and many don't see a dentist until there's a real problem.
The Academy of Pediatric Dentistry says 25 to 35 percent of kids between the ages of 2 and 5 already have tooth decay.
But most kids don't have their first dentist visit until they are 2.
"Going to the dentist is not top of mind. You think about vaccinations and well visits and getting proper nutrition and learning all about that," says Dr. Paul Casamassimo, of Nationwide Children's Hospital in Columbus, Ohio.
Even then a small cavity can create lasting problems.
"If a child experiences tooth decay in their baby teeth, they're more likely to have tooth decay in their permanent teeth. So, it begins a process that's very difficult to stop," Dr. Casamassimo.
The Academy has just changed its guidelines, advising parents to take children for their first dental visit at 1 year of age.
Start early with tooth brushing and flossing.
And limit sugar.
"We know that frequency of sugar exposure is really what causes tooth decay in kids. So if they're constantly exposed to sugar throughout the day, it's a greater likelihood that they're going to get tooth decay," says Dr. Casamassimo.
