The recommended doses of fluoride for children in places where the water has less than 0.3 ppm of fluoride (i.e., Plumas country) are:
Birth to 6 months: 0
Age 6 months to 3 years: 0.25 mg daily
Age 3 to 6 years: 0.5 mg daily
Age 6 year up to 16 years: 1 mg daily.
If your older child (up through 16) is not taking fluoride, just ask for a prescription the next time you're in.