This is one of the symptoms of Irlen Syndrome. Parents if you find your child frequently does not recognise words after working them out several times on previously pages you need to take action. First a visit to your local optometrist; this should be covered by medicare. If there are no major problems then follow this with a visit to an Irlen practitioner. You can find the nearest one to you at www.aaic.org.au or in your search engine eg Google; put Irlen your state and your town or city.
If your child has Irlen syndrome they can be helped with coloured overlays, coloured paper or best of all coloured glasses (Irlen specifically modified tints). A good page to find out more about Irlen Syndrome is www.irlen.com