Q. My husband and I have a beautiful 4 1/2-year-old granddaughter. Our son is not married to the mother. Our granddaughter is very loving, active and social, but she bites her nails and at night she grinds her teeth. She lives with her mother, and sees her father often. Should we be concerned?

A. Both habits you mention are common in young children.

Estimates suggest that between 30 percent and 60 percent of all children and teens bite their nails. Some researchers believe that nail-biting has a genetic component -- it may run in families. Or it can be imitational -- if a child sees other people biting their nails, he or she may begin.

On the other hand, teeth-grinding in children often has physical causes, such as baby teeth that aren't completely aligned, pain or pressure from new teeth coming in, or pain from an earache.

Stress is another possible cause of both habits -- for example, stress from a major change in the child's daily routines or something that may be going on in preschool. In the latter case, a conversation with the preschool teacher may be warranted.

Here are some other ideas:

• For the nail-biting, avoid scolding or nagging. Help your granddaughter become aware of the habit, and, when you sense she's ready, help her stop or reduce the nail-biting. You could use a chart-and-sticker reward system, and suggest substitute activities such as Play-Doh, Silly Putty, or a handheld game to occupy her hands. As her nails grow in, you might look forward to getting a manicure together.

• For the teeth-grinding, a consultation with the family dentist is a good idea to make sure the grinding isn't doing long-term harm. With baby teeth it probably isn't, but it's worth checking.

• Talk about the situation with the child's parents. If stress is a factor, together you may be able to come up with ways to lower her stress level at home and in her outside activities.

Meanwhile, keep in mind that your granddaughter seems to be doing well overall. It's always worth investigating potential problems, but sometimes they turn out to be not problems but just normal childhood patterns.