**Study Purpose**: This study aims to see if ondansetron given as an oral film works as well as ondansetron given through an IV (a thin tube in a vein) to stop nausea and vomiting caused by chemotherapy in children with a solid tumor. Both groups also receive a steroid called dexamethasone to help prevent these symptoms. **Study Design**: Children in the study are randomly chosen to get either the oral film or the IV form of ondansetron. They will receive the medicine 30 minutes before starting chemotherapy, and then more doses every 4 or 8 hours as needed for up to 2 days. **Participation Criteria**: Kids from 6 months to 18 years old, who have a solid tumor and are starting certain types of chemotherapy, can join if they meet specific health conditions. Some people can't join, such as those who have vomited recently, have certain brain tumors with symptoms, or have allergies to the study medications. - **Key Points**: - Participants will be randomly assigned to one of the two study groups. - The study will last for the duration of chemotherapy treatment. - Parents or guardians must agree and sign consent forms for their child to participate.