We have a Downs Syndrome boy who serves as an altar server at our church. He never makes a mistake and his parents are extremely proud of him, as they should be.
I hope your grandson reaches his potential, which is far greater then people sometimes think.
There is a Down Syndrome young man who serves at every Sunday Mass here in town. I had him in my child care center when he was four years old. And then substituted in his high school class when I work for the public schools.
I now good friends with his mother too!