Your ideas are good.
The activities depend on the degree of mental retardation and the individual educational plan.
However, at all levels, basic reading, reading comprehension, and math should be taught. Pre-schoolers and early el kids should be read to. Seeing pictures in the book will help with their understanding of the stories. Having them talk about the story would increase their verbal skills. Older students should be encouraged to read as much as they are capable.
Since math skills are also incremental, counting people and objects is a start. By high school, learning to handle money is extremely important.
Another thought --
Unless you were teaching extremely low functioning students, vacuuming and dusting would not be appropriate for high schoolers.
I urge you to spend several hours in various special ed classrooms for the mentally impaired.
What about if I put down a trip to the grocery store instead? That way, both reading and math would be covered as well. They would need todo a shopping list and read the sins in the store. They would also need to work with money.
One thing I remember about neighbors of mine in California who had a daughter with Down's Syndrome. The parents kept her enrolled in school year-round, and they were excited if she could remember her last name, her address, and her phone number from one day to the next. The father told me once that if she weren't in school year-round, she wouldn't remember those things, which he considered part of a safety scenario for his daughter. At the same time, he was amazed at her: She was bilingual -- French and English! She wasn't literate, but she could speak and understand both languages well.
As Ms. Sue said, it all depends on the severity of the retardation in each child. Not all Down's children are the same, nor children with autism or any other condition you could name. Each child has different needs to be addressed; some will progress farther than others.
Your grocery store idea is great!