Preheat oven to 250°F. Grease a large roasting pan. Toss popcorn, Cheerios, Chex, and peanuts together in the pan.
In a medium saucepan, combine brown sugar, corn syrup, and butter. Bring to a rolling boil over medium heat. Boil for 6 minutes, stirring now and then.
Remove from heat. Quickly stir in vanilla and baking soda — the mixture will get light and foamy.
Immediately pour the syrup over the popcorn mixture. Toss well to coat everything evenly.
Bake uncovered for 1 hour, stirring every 15 minutes. Let cool completely, then stir in candy pumpkins.
Notes
Nutrition per serving (3/4 cup): Calories: 216, Total Carbs: 34g, Net Carbs: 32g, Fats: 8g, Protein: 4g.