The tranquility in routine, evening meal of family time, disturbed by a splash. A quiet splash, but one with ripples. Daughter sits, foot bouncing on her chair leg, beating the devil's tattoo. Asks a question that innocently blindsides both parents.

"Mom, Dad, did you ever do drugs?"
The six year old returns to eating. Hesitation, deadly giveaway if not dealt with, in time honored fashion.
"I'm sorry, what did you say, I wasn't paying attention."
Time to think, formulate response, look across the table, but there is no help there. As unprepared as yourself, confirmed with a shrug. As the question is rephrased and expanded upon, your mind races down dead ends. Hypocrisies compete to be chosen as the answer, pick me, pick me! The truth, obviously not the whole truth, but a toned down made for T.V. version? Don't do what I did, do as I say. Possible yet weak, look for better. Alternative, lie. As a potential answer this looks like a promising road, but what about damage control if it fails? Surely the worst thing to do would be to lie and have them find out later. A old friend comes by, remember that time at Glastonbury Festival? Wild times, good times...
"Is that something you are studying at school?"
After all you expect them to be honest about themselves, share anything with you, set an example. Times up, pick an answer.
"No honey, we never did drugs, they are bad for you, you know."
She accepts without question, as you knew she would, and looks back down at her plate. As she eats, her mind will shuffle memories to accommodate this new information, slot it into the complex and ever-changing sentient puzzle. For you, the deed is done and your course is set. Repent at leisure if you wish, but like the lie about premarital sex another year to come, you will not be able to change the path you have just chosen.

"Let me tell you about drugs."
You begin, the lie will need more substance...