Dental fluorosis is also called as mottling of tooth enamel. It is a disturbance of dental enamel caused by the consumption of excess fluoride during tooth development.
Fluoride protects kids’ teeth from cavities and helps reverse early stages of decay. The risk of fluoride overexposure happens at any age but it is higher at younger ages. Too much fluoride during early childhood when permanent teeth are forming under the gums but haven’t erupted can cause dental fluorosis. Fluorosis can range from minor, barely noticeable white spots or streaks to severe discoloration or brown markings.
Drinking tap water is the main source of fluoride and nowadays, children and adults get fluoride in dental care products, toothpaste, mouthwash, and other fluoride treatments. Older people tend to have less whereas, more than 40 per cent of kids between 12 to 15 years old have fluorosis from not serious to mild. As fluoride has increased, this percentage has grown.
Kid’s exposure to fluoride can add up if they are:

Getting extra amount of fluoride in drinking water
Swallowing toothpaste rather than spitting it out
Using a fluoride supplement

Almost 60 per cent of people gets fluoridated tap water in their homes. It might be naturally occurring or might be added at water processing plants. Though, critics say that fluoride in water contributes to more instances of dental fluorosis and may contribute to other problems.
How to minimise dental fluorosis in kids’ teeth:

Fluoride in tap water: First you need to determine that if levels of fluoride are above the recommended level. Your dentist may recommend using alternate sources of drinking water for your child if there’s too much fluoride in your water.
Fluoride in toothpaste: It is important to use fluoride toothpaste to protect kids’ teeth against cavities. But it is important to ask your dentist about guidelines for your child. Many health organisations agree that a pea-sized amount is appropriate for 2- to 5-year-olds and that you must always make sure your child spits rather than swallows toothpaste.
Fluoride treatments and supplements: If your water is not fluoridated, talk to your dentist about whether fluoride supplements are needed.

Analysing the fluoride content for your child can minimise the amount of fluorosis and maximise cavity protection. If fluorosis occurs, generally it will be mild. But still talk to your dentist about the best treatment required for your child.