Nail biting, also known as nail biting disorder or nail biting fetish. It is a bad habit in children, mostly between the ages of 3 and 6. What can cause nail biting, such as the presence of mental tension, and the child’s habits, such as sending the child to daycare or kindergarten, the child is nervous and bites his or her nails. Or children who are more introverted, sensitive, or anxious are more likely to bite their nails. There may also be sleep disorders, anxiety, nervousness and restlessness, and tic disorders, all of which can cause nail biting.