"Learning has...to do with curiosity, exploration, problem solving, and innovation. For example, if a baby encounters a toy she's never seen before, she will investigate to figure out the best way or a number of different ways to use it." - Laura Grace Weldon, Free Range Learning
Essentially, babies, toddlers and preschoolers are engineers. Their natural habits of problem solving and innovation with newly encountered toys are exactly what engineers aspire to do - to discover or create new tools for society to enjoy. The way I look at resources to post here for Pre-School Engineering is to see them as tools, as innovations, or otherwise intriguing as mechanical objects.
I also consider multimedia research important for anyone in this day and age, including preschoolers. For example, when I took my 18 month old son to the zoo I was sure to pack a book depicting animals so we connect what we saw at the zoo to the books we treasure at home. After seeing several animals and matching them to our zoo book my son took out one of our truck books and indicated that he would like to see the excavator. I believe that it was a turning point for him and his relationship with books. They open a whole world to him. Having failed to find an excavator cage, I found a video of one on YouTube for him to see. Again, a new resource for him to experience the wonders of the world. So here provide links to books, videos, iPad apps, and more. Having a well-rounded approach to learning that integrates play, reading, and computer exploration is essential for tomorrow's grown-up engineers.