Here is a great tutorial explaining how computers work. Good for the SmartBoard or to use on individual student computers.
The Science Spot's Kids Zone - Check out this list of resources for your computer instruction. Games, activities, websites, and other online tools to teach keyboarding, history, safety, games, puzzles, and more.
Crazy4Computers -Try out this list of computer-related lessons based on grade level and skill. This is a great teacher-made resource that your class can use independently.
Lessons and Apps
e-learningforkids has a great collection of lessons for kids on computer-related topics. All of them are computer-based and themed. Learn to do keyboarding, use Microsoft applications, safety and more.
At edutopia.org you will find apps for teaching programming in your classroom. Most are free to download and use with your students.