My partner and I have already agreed that when our kids are old enough, we are going to start teaching them about different substances, drug safety, harm reduction, addiction, the pros and cons of using certain things. We are going to be realistic, not just "Drugs are bad, m'kay".
There will come a time when they are old enough (i.e. when they are adults) that they will learn about our drug and alcohol use history. But we've both agreed that it's inappropriate for kids to know that kinda stuff about their parents. We will be honest, where appropriate, if they ever come to us with questions about drugs, but we will neither condone it nor encourage it.