The main causes of thick and black tongue coating in children include the following: firstly, it is caused by moss staining, if children eat black-colored foods or medicines, moss staining often occurs, and parents only need to gently wipe the tongue with a cotton swab; if the thick and black tongue coating of children is alleviated, it means that the thick and black tongue coating of children is caused by moss staining, so there is no need to have special treatment, and the symptom will disappear after the child stops ingesting this kind of moss-staining medicines or foods; secondly, it is due to the fact that children are suffering from a feverish disease with a more serious nature, and if children are suffering from severe bacterial infections or severe encephalitis, which has a very serious fever and a long course of the disease, the children will also develop a thick and black tongue coating.