Hey John, I often lead fellowship with special needs adults. Pattern type songs are the key e.g.

Blessed is the name of the Lord
Holy is the name of the Lord
Jesus is the name of the Lord etc

Father we love you we worship we adore You
Glorify Your name in all the earth
Glorify Your name, Glorify Your name
Glorify Your name in all the earth ...........followed by Jesus we love
Spirit we love

Kumbaya, He's Got the Whole World In His Hands, This Is the Day

Any similar songs with lots of repetition. I sometimes write songs of that type

You might get some help from Google.

Here's an example with repetitive lyrics and actions..........

https://www.youtube.com/watch?v=NJvGQwfmdQM

God Bless,
Don