**Study Overview** This study compares two ways to give a medicine called ondansetron to children who are getting chemotherapy. Chemotherapy can make kids feel sick and vomit, and ondansetron helps prevent that. The study wants to see if ondansetron taken as a film that melts in the mouth (oral soluble film) is as good as when it's given through a needle into a vein (intravenously). Both methods are combined with another medicine called dexamethasone to help even more. **Key Points** - **Study Duration**: Kids will take the medicine for two days after chemotherapy. - **Participation Requirements**: Must be a child aged 6 months to 18 years, with a solid tumor. - **Exclusion Criteria**: Kids who have recently vomited, have certain health problems, or have taken specific drugs cannot join. Children will be randomly put into two groups: one takes the oral film, and the other gets the medicine intravenously. Parents or guardians need to agree for their child to join the study.