clean up after themselves. Maybe "help" with putting silverware (minus knives) away. Help putting their clothes back in their dressers. Putting their after meals dishes in the sink or next.
I am a mean mommy and they don't get rewarded for helping lol.
Let them help with anything they are capable of doing. As for rewards?? I think a child should just be required to do certain chores because it's the right thing to do to help the family. It teaches responsibility.