Everyone knows it's wrong. Just about everyone addicted to smoking is trying to quit. They maintain that it's nobody's business if they smoke or not. You won't be surprised to find them hiding their smoking from you, the way you have been hiding your smoking. They will also be hiding other things they do from you.
Kids know how to emulate their parents.
It's the natural thing to do. You sneak around with your habit and they will sneak around with theirs. The close relationship you'd love to have with them will just never happen. I'm sure you don't need to be convinced that you must quit. After all, everyone who loves you and cares for your family wants you to stop smoking.