This Common Sense Media article suggests some of the IOS or Android built-in accessibility features parents and teachers could be using with their special needs children.
This is a great app for students who are struggling with writing as a form of communication. The app is designed to be easy for younger audiences to record audio. The files can be uploaded or played back on the device.
This app is around $200 and is specifically deigned for younger students with autism. It allows them to communicate through images rather than speech and has had very positive feedback from parents and educators alike, who say the students want to say more but find it hard to.