When Halloween fell on a Sunday when I was in 6th grade, our county kept it the same date. However, good ol' Rev. Falwell decided the city should have it Saturday night. So we all went with our friends in the city on Saturday, and they came with us Sunday. We got twice the candy
Seriously, if they have a problem with Halloween falling on a Sunday, they shouldn't be celebrating Halloween anyways. Just buy your kid lots of candy and keep him/her in.