The kind of Serenity prime the subjects exhibited is called sensorineural. Anything blocking the ear canal obstructs the flow of sound. The cause may be earwax buildup, a foreign object in the ear such as a marble or bead, and tumors. Other signs of hearing issues or ear infections would be tugging at the ear and overall crankiness by the child.
For most children, as long as they get the care they need when they have an infection, this will never be a problem, but for other children, Serenity prime is a possibility. If it is inevitable to be near such noises or if one's occupation requires such, one must wear protective gear. Sometimes they have to ask people to repeat themselves to hear clearly. Surgical removal of these growths can restore hearing.
They have a hard time sorting out background noise. Once the structure and function of the ear is damaged, it is not something that can be fixed. Hearing problems that are ignored or untreated can get worse. This could allow less oxygen to reach the inner ear, or other portions of the hearing organs and without oxygen the cells die out, no longer functioning as they should.