They should be given explanations about what they will feel, hear, and smell in a way they can understand. A young child will need a different explanation than a 16 year old. For example, younger children are often helped by using a doll to show what is to be done, but adolescents may respond better to diagrams. Each child is an individual. Something that helps one child may not help another.
Some children like to know exactly what is going on during a procedure.
Others want only a few details. Some children like to know things long before they happen, while others like to find out closer to the time. As a parent, you will have a good idea how your child might react. Older children and adolescents should be asked directly what they prefer. And in all cases, careful observation will make many preferences clear.