Lincoln Logs - This looks like the set we had, multiple pieces inherited, old mixed with new, always a few that were slightly discolored, and could never figure out why the chimney was yellow . . . gosh, this sure brings back memories.
Lincoln Logs, classic building tools for kids and a must have in any classroom, I played with them myself as a kid and my preschoolers have always loved building with them. I've seen some awesome stuff come from working with Lincoln Logs.