It is certainly important for infants and children between the ages of 6 months and 16 years to be exposed to fluoride. This is the timeframe during which the primary and permanent teeth come in. However, adults benefit from fluoride, too. New research indicates that topical fluoride from toothpastes, mouth rinses, and fluoride treatments are as important in fighting tooth decay as in strengthening developing teeth.
“It is important to remember children should use reduced fluoride toothpaste, and no toothpaste at all for children under 2 years of age unless prescribed by a dentist.”

Fluorosis
A major cause of fluorosis is the inappropriate use of fluoride-containing dental products such as toothpaste and mouth rinses. Sometimes, children enjoy the taste of fluoridated toothpaste so much that they swallow it instead of spitting it out. Do not let your child swallow toothpaste, and ensure they rinse with fresh water afterward, and spit it out.
The most critical years associated with the formation of dental fluorosis lie between birth and age 6 or 7.
Other things can cause fluorosis. For example, taking a higher-than-prescribed amount of a fluoride supplement during early childhood can cause it. So can taking a fluoride supplement when fluoridated drinking water or fluoride-fortified fruit juices and soft drink already provide the right amount.