Engineering is Elementary is a great site for introducing engineering and technical literacy in children. It has curriculum and lesson plans that integrate engineering and technology concepts and skills in elementary science concepts. The lessons can be used in any STEM class or even in literacy and social studies.
There are storybooks to introduce the students to the engineering problem, which they then have to solve in a hands on project.
This is a great resource to bring STEM topics and Project Based Learning to elementary students.
STEM Resources for Educators
Getting Started with Project Based Learning