One activity I do every year as soon as the grass is covered in leaves is a leaf maze. It’s easy and the kids love it! All I do is rake the leaves away from where I want the maze to be. I add dead ends and put in little obstacles. You can be really creative with this if you have the space and time by turning it into an obstacle course in a maze by including logs to balance on and jump over, tunnels to crawl through, rope swings, and/or toy monsters they have to avoid or fight off.
For kids who are competitive, you can put bean bags at one end of the maze and have them race to see who can grab the bean bags and run back to the starting point first.
You can also do this same thing by letting your grass get tall and mowing the grass in a maze design.