Here are some of the things I used to do during my Havest Festivals in Kindergarten (but appropriate for any primary grade). Parents always LOVED it, and kids found it a memorable and enjoyable day.
Children rotated through stations working with adults (I always had enough parents so I didn't have to take a station, was able to roam). Each adult had a class list which they used to keep track of who had visited each station, and which kids to "grab" next. For those who sometimes were not engaged at a station (while waiting to be "grabbed"). I set out puzzles or bins or books, etc. where they were to go until an adult claimed them. The stations:
leaf collage or suncatcher - kids gathered leaves (or you could gather them in advance) and arranged them on the sticky side of clear contact paper. You could either apply another piece of clear contact, or a piece of construction paper to "close it" and form a background. Children made a frame (or I provided frames made from Sunday comics (the colors worked very well!), attached a piece of yarn as a hanger. (I used contact paper for both sides, and had the "frame" already applied so all the little ones had to do was go outdoors to gather the leaves then press them to the contact paper. I had pre-cut pieces of contact (with backing still intact, but with a corner already peeled and folded over so it would be easy to work with when it was time to apply the backing. Older kids would be able to do more of the steps independently.)
Build a scarecrow - (this group did not rotate but stayed with the project through completion, but you could have kids rotate). I solicited all needed materials in advance and the group worked to build the life size scarecrow which we would perch on a bale of hay in the corridor. We used crumbled newspaper as stuffing. Sometimes the head was a pumpkin, some years we used a stuffed brown paper bag.
Leaf printing - children used watercolor paints to paint leaves and press them onto white art paper. We used a little bit of dish detergent in the water to help the paint "stick." Once dry we framed the pictures with construction paper. Very striking results with the pastels of watercolor, even blue!
Leaf rubbings - put leaves under thin newsprint type paper for rubbing with unwrapped crayons.
Bats and owls - children used dry black beans for bats, brown or white beans for owls, have a set amount of time to pick up one bean at a time and push it through a slit cut in the top of an empty margarine tub. When the time was up, they emptied their cups, sorted, counted and graphed how many bats and owls they had put into the cup.
Dem Bones - each child received a packet of Dem Bones candies to sort and graph. Then they got to eat the candy.
Carve a pumpkin - This group also remained with the project to completion, deciding upon the type of face, scooping the seeds.
Food prep - children helped set up the "buffet." Cookie cutter moons and stars of american cheese, scarecrow's brew cider or juice, owls on branches raisins on stuffed celery, owl head grapes.
Beanbag throw - children tried to make their beanbags land on a pumpkin in the "pumpkin patch" I drew on large cardboard or paper. Each year I made a beanbag for each child with his/her name on it...they got to keep it after playing the game.
That's all I can remember right now. I hope it helps! Have fun!