The year before Tax Credits were introduced there was a different non-means tested allowance available which was never advertised by HMRC!!
It is called the Children's Tax Allowance for the Year 2002/03.
If you have not previously claimed this then the deadline expires on 31 January 2009.
Further details and conditions for claiming are attached
www.litrg.org.uk/help/lowincome/selfemployed/taxallowances.cfm#children