Fluoride can be obtained through several avenues. For older children, fluoridated toothpaste is one of the most common ways to directly give teeth a "fluoride treatment." Public drinking water in most cities across America has fluoride added in, a step made decades ago to help children and families receive the fluoride needed to sustain healthy teeth. If your child tends to consume only bottled water, they may not be getting fluoride through this avenue.
Depending on your child's needs, their dentist may suggest that they receive professional fluoride treatment. The FDA and the American Dental Association both approve of this treatment for children as young as six months old. Fluoride treatment may involve the use of a prescription-level mouthwash, toothpaste, or supplement. In younger children, it may be performed as a "varnish" that the dentist applies in the office.