Indigo-Children-Characteristics-What-the-Heck-are-Indigo-Children-Anyway-Photo3Nervous tics are involuntary spasms of different muscle groups. They typically appear at around six years old, and last under twelve months. The onset of these symptoms is caused by age-related peculiarities in the development of the nervous system. Tics in children, such as Trichotillomania, characterized by pulling of the hair, the habit of the persistent biting of fingernails, and even Tourette’s syndrome, occur in all races, cultures and social groups.