Staying on topic—at some point, ask yourself why you would want a spiritually harmful activity to be portrayed as naturalistic and harmless.
It isn't harmless, but it is natural. The truth is the truth, no matter what. And if you tell children that ___ is evil, only for them to find out later that ____ has a logical, scientific, tested, proved basis, you most probably will have eroded their faith.
Children are falling away from church in great numbers as they grow older. Part of the reason seems to be that everything is candy-coated. When they get to high school or college and realize that everything is not so simple. They feel misled and leave.
Telling them the truth, not whitewashing; and taking the time to explain that some things are more complicated than they seem, would seem to be basic to retaining those who fall away. Children especially need the tools to make good decisions, but too often, we treat them as though they won't love the Lord without fancying it up.
There is more than enough evil in the world. Why say something is when it strictly isn't? Why not point to true evil and teach them why they should avoid it. And why not tell them that they should avoid it for another, different reason? Because the appearance of evil is to be avoided too? We are to avoid the appearance of evil. There is a Bible verse that addresses this directly: 1 Thessalonians 5:22 From all appearance of evil refrain yourselves.
There is a natural reason for the phenomenon of why Ouija boards "work". That doesn't make evil something you should want or chase after. Teach people the whole truth and they have a solid foundation. Teach them a half-truth and they do not. Teaching them the whole truth and that the Bible speaks to this exact instance is teaching them that the Bible is full of wisdom that addresses their every need.