Call your local children's hospital or bigger hospital with a children's ward. They are generally connected to one group of dogs/handlers. They can point you in the right direction. That is my next move with my dog . He has done well with mentally challenged adults in that scenario. Outside of the hospital scenario I watched him lay down and let a family of mentally challenged children hug him, pet him, and tell him what to do, he did better then just good.
Misty- Samoyed Mix, Tannor- Golden Retriever CGC
Robyn- GSD CGC, TC, Midnite-GSD CGC,TC, Brennan-Golden Retriever CGC, Batman-Husky/Greyhound , Apollo-GSD