1) Make it easy for everyone. If your child wants to be a skeleton, he/she could wear pajama bottoms, with a taped on cut out skeleton. A painter: could wear a white apron and hold paintbrushes. Children can also use wear just a fun Halloween headband, Halloween t-shirt or a Halloween hat!
2) If your child is scared of the dark, feel free to stay home and have them pass out the candy. If you do venture outside, give your son/daughter their own flashlight. They even make flashlights that go around your neck to avoid holding another item.
3) I find that preparing children ahead of time, about the events of the night can avoid anxiety and unexpected tantrums.
If you decide to go the opposite route and make an elaborate costume, you may want to check out Carter's Halloween costume from last year. The Huffington Post's, "Dad Makes Ice Cream Truck Halloween Costume For Son Who Uses A Wheelchair" By Cavan Sieczkowski
will truly amaze you! Carters father decided to build a Halloween costume around his wheel chair.