It might even be iron stains. Is your child having iron supplements? In any case a clean up is required. Thanks

Need to get scaling or cleaning often.generally goes away with age.if frequent scaling not done may lead to cavities.

Hi. There are a lot of bacteria in the mouth,which are routinely found. They are also present in the plaque which is present on the teeth. Some times some bacteria cause colouring of the plaque which are called as chromogenic bacteria. These bacteria cause black stains on the teeth. They can be removed by routine scaling. You can visit a dentist for the same.