Additional Study Information: Abnormal muscle tightness -known as spasticity- in the leg can happen when a child has cerebral palsy. If your child has spasticity, they may find it difficult to straighten their leg and experience stiffness. The goal of this study is to collect information from participants about the safety and effectiveness of using BOTOX to treat arm and hand spasticity in children. In this study, your child will receive an injection into specific muscles of the leg affected by spasticity. Your child will either be injected with the active drug (BOTOX) or will be given the placebo -which is an inactive substance that has no medicinal effect on your child and is used as a comparison to test the effects of the drug. The participant has a one in three chances of receiving the placebo and this is decided randomly. During the course of this study, your child will have up to 8 study clinic visits. In addition to the clinic visits, your child will also be required to attend weekly standardized physical therapy sessions. These sessions will last for 13 weeks during the course of this study.After completion of this part of the study and if your child qualifies, they may enroll in the second part of the study, in which they will receive up to 5 treatments with BOTOX (at least 12 weeks apart).