This is a condition where a child has consumed too much fluoride over long periods of time before their teeth erupted out of the gingiva.  This is not a disease!!!  This condition is very subtle and will not progress as soon as the teeth erupt.  Classic signs of fluorosis include faint white spots or lines on the teeth that are have no effect on the function or health of the tooth.  To help manage this, make sure to only use children's toothpaste for your child during development to help maintain an appropriate dose of daily fluoride for their age range.

For more information follow the link below

https://www.mouthhealthy.org/en/az-topics/f/fluorosis