Deal with the underlying cause
Understand what is causing your child to bite nails. If you know the reason, then talk to him about it. Address your child’s concerns and help him/her distress. If you do not know the reason, then patiently ask your child about what is eating her. Unless you identify and address the root cause of your child’s nail biting, it will be difficult to break it.
Make him/her aware of the habit
Help your child be aware of it. Once you point out to him that he tends to bite nails often under pressure, ask him how he prefers to be alerted every time he does it. Some kids prefer a physical reminder–like a touch on the arm–some kids prefer verbal reminder. The more aware he becomes of this habit, more likely he will be able to consciously stop himself.
There are many things you can encourage your child to do to let out steam and distress himself. Ask him to spend longer time every day in outdoor playing – this can burn off nervous energy. Also, arrange more time with friends – this can also burn off tension. Or engage him in arts and crafts activities – which will do the dual job of distraction and keeping his hands busy. Teach him various relaxation techniques like deep breathing
Keep fingernails trimmed and clean
Sometimes a hanging bit of nail is what is encouraging your child to bite. Keep his fingernails cleaned and neatly trimmed. This will also reduce the chances of soreness. Also, ask him to wash his hands often
Help him deal with peers’ teasing
Many times, when the child bites his nails, his friends in playground or school would start teasing him. This might make the child more worried, further increasing the tendency to bite nails. Talk to your child about the teasing and encourage him to discuss with you his feelings. This also presents itself as a big motivation for your child to kick this habit.