It sounds like the 14-year-old is wearing a muhapatti (mouth cloth), which is a common Jain practice. Jains use this cloth to remind themselves of ahimsa (non-violence) in speech and to help avoid harming even tiny organisms, by covering the mouth during prayers, talks, or temple ceremonies. While monks and nuns widely use it, lay devotees sometimes wear it during special rituals or temple events as a sign of careful speech and compassion. You can read more about this practice here