In your question: "Does God wish for his children to partake of weed and other narcotic substances, and to what extent?"

Every person has his/her own capacity, the knowledge and experience, the ability to reason and think. Its our choice to choose. We're given free will by God as what you'd mentioned. I don't know if God wishes us to use weed or other substances. I cannot understand God's mind, If we trust God, we can do what we want to do based on our own capacity, the knowledge and experience, the ability to reason and think..And offer our works to God.