Reformation Day occurs on the last Sunday in October.
Sadly, Halloween occurs on the Saturday just before Reformation Day so why not prepare bags of treats now with a good Gospel tract for children inside also. Maybe you could prepare a Christian explanation of Halloween and the Gospel and have this also available for accompanying parents.
Reformation Day, commemorates what was perhaps the greatest move of God’s Spirit since the days of the Apostles. Martin Luther’s nailing of his ninety-five theses to the church door on October 31, 1517, provoked a debate that culminated finally in what we now call the Protestant Reformation. Though preached clearly in the New Testament and found in the writings of many of the church fathers, the medieval bishops and priests had largely forgotten the truth that our own good works can by no means merit God’s favor.
Salvation is by grace alone through faith alone, and good works result from our faith, they are not added to it as the grounds for our right standing in the Lord’s eyes (Eph. 2:8-10). Justification, God’s declaration that we are not guilty and are forgiven of our sins as well as being righteous in His sight, comes because through our faith alone the Father imputes, or reckons to our account, the perfect righteousness of Christ (2 Cor. 5:21).