When they do a fall festival at our church, they have simple carnival games with candy for prizes that are easy to make. One is the fishing game - dowel rods with strings and a clothes pin - someone hides behind a screen and clips little toys and candy to the clothes pin, throw a ball to knock over cans or roll it like bowling, pick up ducks floating in a bucket of water that have numbers on them for the prize you win, throw a ball or football (can be a nerf ball) through a target, ring toss or bean bag toss. Also you can have them drop clothes pins into a bottle, bob for apples, etc. Let the older kids run the games. One of the games that the kids really enjoyed was crush the can - someone had one of those aluminum can crushers that help you recycle cans or you can just use a hammer. Great if you recycle - just save your cans and let the kids crush them for you to make them smaller.
The other thing that my kids have always enjoyed at their parties are large boxes to crawl through or make a fort out of. Find a furniture store or appliance store near you and ask them to save you boxes. My kids would tape them together and I would use a box cutter to cut windows and doors. They would blow up balloons and put them in one of the large refrigerator boxes to make a "ball pit." Almost as much fun to make as it is to play in, especially for your older kids.
Google for costume ideas like Addams family, Wizard of Oz, Alice in Wonderland, group of superheroes, Santa Claus and Mrs. Claus with elves or reindeer, etc. Just depends on what your family likes and how elaborate you want to make the costumes.
I like the more creative things like you and your husband could be artists and your kids could be the "creations" - dress them in white and have paint all over them. Or you could be the solar system - Mom (or Dad) as the sun (dressed in yellow) and all the others as the planets - dressed in various colors that represent each planet like red for Mars and maybe even paint some planet looking designs on their clothes. Saturn would have rings around them, etc. Dress like different candy bars, deck of cards, dominos, etc. It is really best if it fits your family's personality. Have fun!