OP, Halloween is "All Hallow's Eve," the vigil of All Saint's Day, a Christian feast day. Google "Catholic Halloween" and you'll get the full history of the holiday. Lots of interesting facts about the origins of trick-or-treating and jack'o'lanterns.
The occult has certainly crept into the day, but it is far from the actual meaning of the day. There is no requirement that your child celebrate evil or gore! Let it be the sweet American childhood activity of neighborliness and fun, and if you like, add some Christian elements, such as praying for the souls of the deceased, or reading about a saint's life.
FWIW, my kids often dress up as their favorite saints
