Where can I download free educational software for an interactive whiteboard for 5-7 year olds?

Hi, I'm a learning support istant in a school for autistic kids, we desperately need some free software to use with our interactive whiteboards, we've blown all our funds on the boards themselves! We're not just looking for autism specific software, any literacy, numeracy resources, anything just so we can make teaching the little dudes more fun. Thanks very much ladies and gents and rock on, Lawrence.