There are probably a number of reasons why children bite their nails. They can be bored or anxious about something. Maybe it's just a habit they picked up. Children find ways to deal with stress and nail biting is common.
Our five year old is constantly biting her nails. Sometimes she bites her nails so bad that her finger tips are sore. My husband bites his nails too, so she could have learned it from watching him. She recently changed schools and had to make new friends and get used to a new teacher. She seems to like her new school and friends but it's a different environment, so that might be a trigger.
We always advise her to stop biting her nails because we don't want her to hurt herself. My husband and our daughter are trying to help each other break this habit. Whenever she sees him bite his nails she tells him to stop and vice versa. We don't punish her or nag her as that will probably makes things worse. When she is ready to stop biting her nails we will be here for her.
What do you do when you're nervous?