You should teach your child to crochet or knit. When they are occupied with creating things out of yarn, they will not remember to bite their nails, and their hands will be too occupied to do something else.
Give children lots of toys to play with. Play games with them, games that are keeping them far from biting their fingernails. As you know, children are very creative so harness their nervous energy.
Take your child to get a professional manicure. This procedure is sometimes a good one; its easier to stop nail biting when your fingernails look really good and nice. At the very least, it can be excellent mother-daughter bonding time! Dont you think?
Use bitter nail polish. You can find it at almost drugstores. This nail polish is clear and also a litte bitter, so that once the fingernails go in the mouth, the child (or even adult!) tastes a very unpleasant flavor (but harmless), reminding them not to do it again ever.
Do not punish your children for nail biting.
Children find it not easy to stop a habit, just like adults, even if they are aware that it is a bad habit.
You can use some encouragement and compassion, rather than harsh and difficult punishments.
If you are worried you should take your child to the doctor .
If the nail biting seems like a sign of a high level of anxiety, you should talk to your child, and take him/her to the doctor if you think you need help.