If your school's budget allows, plan a preschool field trip to a local construction site. Preschoolers can see dump trucks and other construction equipment up close, learn about how they dig and move earth, meet and talk with construction workers and discover how they perform their jobs and view buildings in the community that are currently under construction. The preschoolers could even wear their own hard hats and have lunch with some of the construction workers, enjoying the title of "construction worker for the day."
Have your preschoolers construct their own building (a skyscraper, perhaps, or any building they choose, such as a school, church, or store) in the preschool classroom. Building materials could be cardboard "bricks" or even real wood (plan for adequate adult supervision when using these tools). Teach your preschoolers how to use a tape measure to measure boards, what makes a building stable and strong and how towers are built (introducing the concept of, "Why don't they fall over?"). Some preschoolers could be in charge of the building's "landscaping," drawing bushes, trees and flowers on graph paper to make the building's landscape pretty (a good opportunity for a lesson in helping the environment). Counting the building's windows and floors and working together as a building team are just two of many skills preschoolers can learn during this activity.
Arrange for various construction equipment to be on display in the preschool's parking lot (if space is available). The local highway department could bring some dump trucks and a snowplow, for example, and a local builder could bring a bulldozer and a backhoe. Preschoolers could climb up and sit inside the equipment and listen to presentations from different members of the construction community and have a class group picture taken in front of the equipment. They could learn about the different parts of the construction equipment, what they're used for, and how to stay safe around construction equipment. Preschoolers could even receive a "construction site safety certificate" at the end of class.