3rd grade might be a bit young, but you can make simplified version of the 4917 computer https://punkx.org/4917/ https://punkx.org/4917/ and make few funny self

3rd grade might be a bit young, but you can make simplified version of the 4917 computer https://punkx.org/4917/ https://punkx.org/4917/ and make few funny self modifying programs they can "compute" on pen and paper also maybe get few examples from human resource machine and play them out, this might be more fun than pb&j https://tomorrowcorporation.com/humanresourcemachine https://tomorrowcorporation.com/humanresourcemachine