OCD is a type of anxiety disorder. A child with OCD has obsessive thoughts that are not wanted. They are linked to fears, such as touching dirty objects. They can uses compulsive rituals such as hand washing to control the fears. These rituals may feel rational or irrational to the person doing them. He/she may not understand why they do these rituals. They may feel embarrassed that the behaviors occur and can't be controlled.
OCD affects children and adults alike. They however look different on different children.