My twins were born on Halloween so this is something I can speak of!!
For their 2nd Bday, we did a full out costume party. I was lucky to rent a room at a meeting house so we had tons of room.
We had a couple 4' tall inflatable halloween things (smaller versions of the blow up santas and such you see on front lawns during holiday season) and we used these as decoration.
I also had an inflatable tube/little house thing that we inflated and the kids got to crawl thru and play in the house/fort part. (it was about 8' end to end).
We too got mini pumpkins and let the kids color them with markers (crayons don't work) and let them take them home. We played pin the nose on the pumpkin -I took a big poster board and colored a pumpkin on it without a nose and then cut out a bunch of construction paper noses and simply used tape and let the kids play without blind folds - too young for that.
I'm a planner but for this I knew it was better to just keep it simple and let them play. Since we had such a good size room, they got to run and play without running into furniture.
I made food for the adults and of course a cake (did a castle since my boys were dressed as Knights) and had tons of fruit and veggies/dip and of course goldfish crackers and nuggets for the kids.
It worked out quite well.
We did photos (for the kids that would sit still!) next to one of the blow up things (a cool looking black cat sitting on a pumpkin) and they turned out really great.
Just take a lot of pics, have lots of wipes, and enjoy it. As they get older, you can plan more of course, but for now, just dress them up real cute and have extra camera batteries!
Enjoy!
J.