Forget about touch screens until your child has had a proper access technology assessment.
There are many types of dyslexia and learning difficulties and numerous pieces of software and hardware to help.
Does your child have reading and writing difficulties? Does he or she have a preferred font size, colour background and line spacing when reading either printed or screen text?
There are big print keyboards available which can be simplified for someone with learning difficulties.
So, the first step is to get your child statemented by the local educational authority. Then get an assessment by an expert. This assessment if properly carried out will address all the needs and offer possilbe solutions.
The Disabity Discrimination Act makes it illegal for schools not to make reasonable adjustment for a student having learning difficulties.
Hope this helps.