Acetaminophen, Administration, Oral, Analgesia, Epidural, Analgesics, Analgesics, Opioid, Cerebral Palsy, Child, Child, Preschool, Cohort Studies, Drug Administration Schedule, Female, Health Services Needs and Demand, Humans, Ibuprofen, Male, Morphine, Muscle Spasticity, Pain, Postoperative, Retrospective Studies, Rhizotomy