My toddler has a little grey spot on his tooth. anyway to get fixed?

Depends: It depends on what that little gray spot is. It sounds like a cavity and should be checked out by a dentist. The dentist should be able do a filling and remove the gray spot. If your dentist is unable to work on your child they may refer you to a pedodontist.

In or out: Different treatment if it is internal or external. Stain can be polished off, if it is a dead tooth, it will need root canal or extraction.