N.P.
My little girl has been taking iron supplements since she was born because she was premature. She doesn’t have teeth yet but her split-up has become a stain bomb. We combat that by immediately taking the spit up on clothing and hitting it with a stain remover and washing it.
Can’t really do that with a toddlers teeth as bleaching agents are out of the question, (don’t want him to swallow it!) so I’m not sure what you could do to get rid of the stains that are already there, but to help prevent future stains, as soon as he is finished taking his supplement brush his teeth! Just like it is suggested if you are a heavy coffee drinker to brush your teeth to help prevent stains after consuming, I’m sure the same good advice would help keep an iron supplement stain from settling as well.