In the 23 years I have been in practice, the recommendations about fluoride and children has changed. Although there is great deal of information supporting the safe use of fluoride to prevent tooth decay, recommendations about how much and how often have frequently changed. Here is an updated description of the current recommendations.
One note: you can find a lot of misinformation on the Internet. And a great example is the misleading, non-scientific, and sometimes outright false and outrageous anti-fluoride information on the Internet. Do not believe this misinformation. It safe to use fluoride to prevent teeth decay.
The current recommendations:
1. It is helpful to have your child drink fluoridated water and to cook using fluoridated water. In Central Ohio, our public water supply has fluoride added. Drinking bottled water does not reliably give enough fluoride. Most household water filters do not remove fluoride, but it is worthwhile making sure (by reading the filter's information).
2. Once babies have their first teeth, brush their teeth daily with a grain of rice sized amount of fluoride containing toothpaste. Once they reach 3 years of age, it should be a pea sized amount of fluoride containing toothpaste.
3. Routinely see the dentist by 3 years of age, sooner if recommended by the pediatrician.
4. Fluoride varnishes are recommended once a number of teeth have extruded. We now do the fluoride varnish at 18 month, 24 month, and 30 month check ups. The kids seem to be tolerating it just fine. The varnish stays on your teeth for 4-6 hours. During those 4-6 hours, it is best to maintain a soft diet and avoid hot liquids. Do not brush or floss during that 4-6 hours after the varnish (you can resume normal dental care the next day). If you take supplemental fluoride, stop for 3-4 days after the varnish is applied.
If you interested in reading more, here is a link to more information from the website Healthy Children.