Ask The Doctor: Child Twisting Hair

I have identical twin girls that are 2 1/2 years old. One of my daughters tends to twist her hair quite often lately. She has been doing this for several months. She twists it into knots and it has gotten so bad that she has very thin hair on the crown of her head. Is there anything I can do to help her stop this? She mainly does this at naptime, bedtime and at down times during the day, such as when she is watching a TV show.

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