Do we have to explain the contents of the information we send to the individual?

The GDPR requires that the information you provide to an individual is in a concise, transparent, intelligible and easily accessible form, using clear and plain language. This will be particularly important where the information is addressed to a child.

At its most basic, this means that the additional information you provide in response to a request should be capable of being understood by the average person. However, you are not required to ensure that that the information is provided in a form that can be understood by the particular individual making the request.