We live in a society where it has become common to face the spiritual with skepticism or indifference. Even in the Church it is not uncommon to find even priests who deny the actual existence of Satan, angels, or demons. Often these same people deny, if not the existence of sin, its power to eternally separate us from the presence of God.
This has resulted in a situation where our youth are exposed to many false and dangerous beliefs. Some of these beliefs are considered harmless or even silly by secular culture, when they are in truth dangerous. Dangerous to the soul and sometimes even dangerous to the body.
Take Wicca. Basically a made up religion with its historical origins in the 19th century. Based upon vague fantasies of a non-existent ancient witchcraft Wiccans themselves do not believe that they worship the devil. However many do call upon powers from beyond this world, attempting to affect happenings in the physical world through the exercise of power.
Now there is a real spiritual world. It is a plane of existence inhabited by the angels and demons, that is fallen angels, and includes the heavens and hell to which those who die go awaiting the final coming of Christ. There is a power in this spiritual world. It is the same power that exists in the mortal plane. The power of God. But God also allows other forces to reach from that plane into the world. Some actions occur through His own power, as when God answers a prayer, or allows the Blessed Mother or a saint to appear to a mortal. Other forces God also allows to enter the world, as when Satan is allowed to tempt the living or when a demon is allowed to possess a person's body.
It has become unfashionable to talk of such things, but they are as much a part of our Catholic teaching as the Sacraments or Original Sin. It is true that not every mentally unstable or epileptic individual is "possessed." But just as most wild bears are not man eaters, that does not mean that there does not exist a man eating wild bear or two. It also means that its a bad idea to dance with the bears.
So in the present secular world its very likely that if you work with a youth group that some of the members of the group have friends who are either dabbling with Wicca or even from families where it or other pagan practices are considered the norm. It is also likely that they have been exposed to Ouija boards, tarot cards or other spiritually dangerous items.
Think this is a silly thing to worry about? Let's look at it this way. Do you believe in the efficacious power of prayer? That is, do you believe that praying to God or to the Saints or the Blessed Mother actually has the result of causing an effect in the physical world? If you do is it then unreasonable to believe that Satan and his fallen angels can also respond to "prayer." God has allowed Satan power in this world, at least until Christ's second coming. If someone is using an object or ceremony or ritual in a way to reach out to a higher power, and the intent of that individual is not directed toward God then does it not make sense that another power could respond?
Even if such a power does not manifest physically it is dangerous to soul to dabble with such things. It is especially dangerous for the young, those who are not fully formed in their faith and the weak willed, those already seeped in sin, to fool with such things.