What does it mean if a child's baby teeth have dark spots?

It usually indicates that the deciduous teeth either have defects in their enamel or are developing decay. I usually recommend that parents of young children inspect their teeth to look for these. If a parent does notice any 'dark spots' a visit to the dentist is in order.

Young children can develop decay in their deciduous teeth even before the age of three and The American Academy of Pediatric Dentistry recommends that a child's first visit to a dentist be no later than their first birthday.