I just googled mongolian blue spots:
Mongolian spot - Wikipedia, the free encyclopedia
A
Mongolian spot, also known as "Mongolian blue spot," "Congenital dermal melanocytosis,"
[1] and "Dermal melanocytosis"
[1] is a
benign, flat,
congenital birthmark with wavy borders and irregular shape, discovered on and named after
Mongolians by
Erwin Bälz.
[2][3] It is also extremely prevalent among
East Asians,
Polynesians,
Native Americans, and
East Africans.
[4][5] It normally disappears three to five years after birth and almost always by
puberty.
[6] The most common color is blue, although they can be blue-gray, blue-black or even deep brown.
Origin
The Mongolian spot is a
congenital developmental condition exclusively involving the
skin. The blue colour is caused by
melanocytes,
melanin-containing cells, that are deep under the skin.
[5] Usually, as multiple spots or one large patch, it covers one or more of the lumbosacral area (lower
back), the
buttocks,
flanks, and
shoulders.
[5] It results from the entrapment of melanocytes in the lower half to two-thirds of the
dermis during their migration from the
neural crest to the
epidermis during
embryonic development.
[5]
The condition is unrelated to sex; male and female infants are equally predisposed to Mongolian spot. The spots are harmless.
[5] However, recent research has shown that Mongolian spots may occur more commonly in children with certain rare metabolic conditions, such as
mucopolysaccharidosis,
Niemann-Pick syndrome and GM1
gangliosidosis.
[7] Among those who are not aware of the background of the Mongolian spots, it may sometimes be mistaken for a bruise, possibly resulting in unfounded concerns about abuse.[8] Prevalence
Rough estimates are that the Mongolian spots are most prevalent among infants of
East Asian groups. Infants may be born with one or more Mongolian spots ranging from small area on the buttocks to a larger area on the back. They also occur in about 90-95% and about 80-85% of East African and
Native American infants, respectively.
[4] Approximately 90% of Polynesians and Micronesians are born with Mongolian spots, as are about 46% of Latin American children (those who have some sort of Native American ancestry).
[9] These spots also appear on 1-10% of babies of full Caucasian descent.
[4] [edit] Cultural references
The Mongolian spot is referred to in the
Japanese idiom (to have a) blue butt (尻が青い
shiri ga aoi?), meaning "
wet behind the ears", young, inexperienced.
[10][11] In
Mongolia, Mongolian spot is mostly called "blue spot."
Is the boy of eastern Asian decent? Seems like it would be more likely to be true if he is. From this article, seems like they are just birthmarks, and not a "condition" like cleft palate like another child has. For example, if I had a child with a large birthmark, I wouldn't mark it on the sheet, just as I wouldn't if they had like a huge mole or something. However, the boy did say his mom hit him. That's still concerning.