If you are a teacher, I'd like to tell you this. Give your students their own bricks and cement. Let them do with it whatever they like. They might even just throw them away and go looking for trees with the ax they borrowed from their friends. Don't be upset about it.
If they do take the bricks and cement they are offered, don't give your building plan to them. If you can, share with them your building plan and construct the buildings in front of their eyes. But if you cannot do that, throw away your plan or just hide it from your students.
If you are a parent, substitute "kids" in place of "students" in these paragraphs. Because parents are the first teachers of every kid.