Consent and Assent
When potential participants decide that they are interested in taking part in a study, they begin discussions with various members of the scientific community who are also involved in the study. Once potential participants understand what it means to be in the study and what the possible risks and benefits are, they indicate their willingness to participate by communicating their agreement and signing a document saying they agree to take part. This process is called giving consent.
For children or others who are not legally able to provide consent, a parent or legal guardian provides permission for the person to participate. Even though a person may not be legally able to provide consent, they are still informed about the clinical research to the degree that they are able to understand. They may also have the opportunity to provide their agreement to participate in an alternative way that includes the process of assent.
This information sourced from : http://www.nichd.nih.gov/