Good question!
Absolutely do NOT let your child's dentist to fill up some mercury amalgam (gray fillings). It is a well known toxic that create health problem later in the life. Best to fill with a clear plastic fillings.
Do NOT believe your dentist if he said that the amalgam is safe - he is deadly wrong. Find a good and honest dentist who really understand about the issue.
White pure plastic filling is good. I have the whites on my fillings, and I never have that problem for 6 years. Clear fillings are safe. The news came in about the clear fillings, and that was last year or this past spring.
There is a problem that a few dentist companies mixed with amalgram and plastic fillings. This one I really do not understand because they want to make a profit. You have to make a best judgement and get more info about the plastic fillings.
You as the parent if you have the mercury fillings, then it is unfortuante that you need them to be removed. Look up on google about the amalgram removal. It takes a very long time to get rid of mercury out of your body - perhaps 10 years or more. You can ask your doctor for a mercury blood test that tells you how much mercury in your body.
If you do not believe me, guess what at a school lab if someone spills a mercury liquid in the classroom, all students in the entire school are immediately leave the building until the firemen clean it up. This is not a joke. A perfect example a federal law, officially, prohibits all mercury thermometers in all stores.