The Better Health Channel (Victorian Government) also has a very large amount of information about sleep, sleep problems and what you can do if you are having problems with sleep. http://www.betterhealth.vic.gov.au/
When children breathe through their mouths during the day chances are that they also breathe through their mouths at night. Mouth breathing at night is directly connected to altered levels of carbon dioxide and oxygen in the blood stream. When less oxygen is able to reach the brain, learning and the ability to focus at school becomes a problem for many children.