Is it mandatory to agree to participate in a clinical trial?
It is not mandatory. Parents and patient are free to decide. They will be given information to study, read, question ... and to take the final decision with time and help.
If you accept to be part of a clinical trial, documentation will be given to you to sign. In the case of children under 12, parents or legal guardians are the ones who must sign this documentation to agree and give permission to participate in the clinical trial. This document is called informed assent.
It is possible to change your mind and/or leave the clinical trial without giving a reason. This will not affect the patient's subsequent medical care and no one is going to be bothered about it. It will never affect the treatment that you may receive.