Touch Autism is a brilliant website which lists great apps on iOS and Android for children with Autism Spectrum Disorders, Down Syndrome and Special Needs. 

In their own words;

Touch Autism began to build mobile device applications for children diagnosed with autism spectrum disorders, Down syndrome, intellectual disabilities and other special needs after discovering how incredibly useful this type of technology can be.

Some of the many advantages of these apps are that they suit visual learners, they allow for non-verbal and non-written responding, they provide immediate and consistent feedback, and are very motivating, because they are just so much fun!

Having used a couple of their apps over the past few months I can say that there are some excellent tools here... have a look and enjoy!