Since young children love to stop at construction sites, the next time you have the chance, stop and observe a construction site and watch the progress of a new building being made. Even better, observe the site over a period of time so your child can see the building process.
For a different perspective, walk around finished buildings, like your own house or apartment building. Talk about the parts of the building and the materials used to make them.
Then, provide your children with appropriate materials (such as large boxes and stiff cushions) and invite them to build their own house or castle. Enjoy watching their building go up. Use the opportunity to talk about how their building is like the buildings you have seen.
If your children enjoy this activity, on another day, provide different building materials. Invite them to talk about which ones were easier and/or harder to build with.