They occur in around 80% of Asians, and 80% to 85% of Native American infants. Approximately 90% of Polynesians and Micronesians are born with slate grey nevus, as are about 46% of children in Latin America, where they are associated with non-European descent. These spots also appear on 5–10% of babies of full Caucasian descent. African American babies have slate grey nevus at a frequencies of 90% to 96%.
Both my son and daughter had Mongolian spots when they were really young.
The daycare my son goes to pulled me aside one afternoon while I was picking him up and accused me of hitting him. They thought the mogoilian spots he had on his arse were bruises from me hitting him.
I told them, no they are in fact moglian spots, and him being part asian means it's a very common thing.
I got up her for not having noticed this before. My son had been going to the same place with the same workers since he was 6 months old, he was 3 when they thought it was bashing him. This woman and her co-workers would have changed his nappy 100's of times.