Addiction is one of the most complex emotional issues we can try to cope with. Parenting is simple, parenting an addict is difficult!
You were not the one who used the chemical, they did. You were not the one who took the risk of possibly becoming an addict; they did. While no one is perfect all we can do is try to amend any wrongs we committed but we have to be conscious of the fact that righting our wrong will not change the current reality. The illusion that we might have contributed is problem is a falsehood; unless you got them high!