No, your child will not be a better musician after attending one of the many summer music camps. However, your student would also not be a better basketball player the week after attending basketball camp. Yes they will spend the week involved in an environment customized to help their musical growth. Music is a lifelong journey and marked improvement takes time.
For instance, some of the technical skills they learn will require thousands of repetitions to become muscle memory. There's literally not enough hours in a day for them to master these new skills and techniques in one week.