Following the most up-to-date guidelines by the American Dental Association, you may start using a tiny smear of fluoride toothpaste as soon as the first baby teeth erupt. By 3 to 6 years of age, the amount should be increased to a pea-sized dollop. Parents should supervise brushing to ensure the proper amount of toothpaste is being used. Children naturally want to swallow toothpaste after brushing, and swallowing too much fluoride toothpaste can cause teeth to stain.