There are many resources available for teaching students about computers in the elementary grades. These pages are organized by grade level and subject matter for ease of use.
This website is one I use in my classrooms, PK-6 grades at the school where I teach. Students are taught to use the keyboard, as well as work on a variety of applications. Sometimes, there are moments when we can use a "Sponge Activity" and some of these sites come in very handy for that.