Actually, moderate to high functioning children on the autism spectrum are `aqil and should be expected to pray just like any other Muslim child. Consequently, One should teach his/her autistic child to pray at the age of 7 so that by the age of 10 it becomes a habit.
In fact, the repetitive motions of the prayer might even be soothing for your autistic child. A lot of children on the autism spectrum experience challenges with sensory overload, and the prayer might have a calming effect.
Furthermore, there is healing in Allah’s words, so one’s autistic child could both learn the Qur’an and hear it being recited.
If they can perform all the activities of prayer they can of course pray and have to pray. But if their autism doesn’t allow them to understand what prayer is and limits them from performing the necessary acts they are forgiven.
To know more about the autistic children with prayer, watch this important talk with Sheikh Waleed Basyouni.