My daughter is born October 24th, and we were SO hoping it would have been Halloween!! :) But we celebrate it that way anyway!! :)
We have bought pumpkins for the kids to paint with markers as their take home gift...that was big fun! And it can be pretty big pumpkins...for like $3 each if you find the right place! I put the kids names on the stems with tags so there wouldn't be any fighting over who's was who's pumpkin! (buy the pumpkins with stems for that). This year...we're going to do something like a "pumpkin hunt" which is like and Easter Egg hunt with the small pumpkins around the yard! Give each child a pumpkin basket to fill up with those...the pumpkin basket can be the take home gift ($1 at walmart).
I used colors of orange and purple to decorate...a little black in there too, but I thought orange and purple were a little less "Scarey" for a bday party. I also just bought the Halloween paper plates/napkins with orange & purple on there...those you can find anywhere now! Mine had pumpkins and withces on them for a girl...but I'm sure there are pumpkins and mummy's or dracula or something!
We got a cake of course, and just had a pumpkin on it...with a bday hat on his head!!
There is So many fun things you can do!!
Also...try googling "halloween birthday party"...and you can scan the internet for great ideas too!!
Good luck! Happy party planning!
L