Sleep-Related Rhythmic Movements (Pediatrics): Sleep-related rhythmic movements are involuntary movements that can be seen often at the beginning of sleep and sometimes during sleep or waking up, affecting large muscle groups in the head, neck, and trunk. It is frequently seen in infants and children and usually disappears with age. These are quite normal conditions, but if the child injures or their sleep is disrupted due to these movements, it is called sleep-related rhythmic movement disorder and may require treatment.