When the world became a global village then it became imperative to be aware of the things happening even in the other distant corners of the earth. Like Halloween celebrations. And to those who are in west the requirement is even more expedient. Shaikh Omar Subedar has already done the needful in this case at Mathabah. please have a look at this post.
In case you are hard pressed for time and want a shorter answer then the conclusion is as follows. Halloween in an old British/Irish/Celtic practice/tradition/celebration originating in polytheism and superstition. If your children feel left out of the fun and action when they see all the bonhomie going around them then cajole them about the benefits of patience and steadfastness.
Verily Lord Most High is with the patient and steadfast.
And All Praise is for Lord Almighty for having put such brothers and sisters at the right place who clarify such matters for us.