It is interesting how in this thread the feeling of what one thinks would be ok weighs more than what is actually permitted. I have read many materials from yeshivos and day schools warning us not to participate in this holiday for numerous reasons, including giving mixed messages to our children and the other Jewish children in our neighborhoods.
I imagine tossing candy to a youngster for Halloween may be a participative act that has some non-Jewish meaning like throwing salt over your shoulder or knocking on wood. Really, Halloween is not worth us having anything to do with.
Thanksgiving, too, has to be looked at carefully. There is a definite hashkofa on when/if someone should sit down to a dinner the same time each year to eat a turkey. Maybe someone knows more about that.