Younger siblings watch much more carefully than they listen. Whatever you tell them gets filtered through what they have seen you do, and the doing wins every time, including the things you would rather they had not noticed. You did not sign up for this and it happens anyway. Being watched is not the same as being responsible for their whole life.

Pick one thing you would want them to copy and do it visibly this week, without making a lesson of it. If they have seen you do something you regret, say so plainly, since that is also worth them seeing.