The study, by the Centers for Disease Control and Prevention, said nearly 40 percent of children ages 3 to 6 used more toothpaste than recommended by dental professionals. For young children with emerging teeth, swallowing too much fluoride toothpaste can cause discoloration of their teeth, a condition called dental fluorosis.

Parents of children in that age bracket should squeeze no more than a pea-size amount of toothpaste on their brush, the C.D.C. and American Dental Association recommend.

The C.D.C.’s survey of nearly 1,700 children in that age range found that about 38 percent of them used more than the recommended amount of toothpaste, which has the potential to exceed the daily recommendation of fluoride intake. Exceedingly high concentrations of fluoride in drinking water can also contribute to dental fluorosis, the dental association says on its website.