Engineering Interact is a great site to introduce engineering concepts and processes to 9-11 year olds.
The site has 5 different games based on different science topics that give students a chance to learn while playing. The games teach students about the concepts. The concepts are: Light, Sound, Forces and Motion, Earth and Beyond, Electricity.
There are also links to other resources about science and engineering.
This is a great resource for younger students, but the games can be used with older students also.