A book which seems to understand perfectionism very well and which many find supportive is What To Do When Good Enough Isn't Good Enough. Another book you might like is Perfectionism: What's Bad About Being Too Good. While insightful, these are written gently for kids, in a style that is fun and engaging. With any of these books it may be wise to pre-read and decide if it seems to be a helpful tool to use in guiding the children you have in mind.
Procrastination can be closely related to perfectionism.
