You could have the birthday olympics. Seperate the kids into age groups like 3-5, 6-8, 9-11. Then have different tasks and activities for each group. Like beanbag toss (cornhole)and long jump for the littles, egg toss and potato sack races for the mediums, and obstacle course and three legged race for the bigs. Everyone wins a prize for competing with special prizes for 1st, 2nd, and 3rd.
You could do a scavenger hunt. Assign a big kid to each little or seperate them into two teams and leave riddles leading them to the next clue until they find the big prize - maybe a pinata - at the end.
For the craft you could decorate pumpkins or carve pumpkins (1 pumpkin per family). You could have a make your own pizza station with flattened biscuits for the crust and a number of toppings or decorate your own cupcake with white a chocolate cupcakes and a few colors of frostings and sprinkles and such.
Hope this helps.