It’s not just sleeping that can be difficult, it’s also the getting-to-bed and the waking-up.
Here are some links to help you with all three.
Comprehensive information from the RaisingChildren.net.au site.
Information on sleep in other age groups is also available
Check out tips and tricks in the cool stuff section for useful tools
Several tools and common pitfalls when using them, by the Director of the Yale Paediatric Sleep Centre
An app to improve well being by helping improve sleep
This site is American but sensibly summarises the benefits, risks and how to use melatonin most effectively.