With younger children, I often get them to draw a monster, which we call the Nervous Monster. Then we talk about how rude he is to interrupt their lovely performance by making them nervous.
But it got us having more discussion about the causes and effects of anxiety on the performer. Does anxiety affect the performance or does a poorly prepared performance bring on worse anxiety?
We all know preparation is the key to performance, but do we think about how to prepare?
Get to know your material. Key, chord progression, patterns of phrases. Play at different speeds, breaking music into sections and starting at random sections.
Practise infront as many people as you can. Also record yourself.