Oh man, theme parks and Halloween are like peanut butter and chocolate for me; good on their own, but work sooo well together!
First true memories would be of some of the Fright Fest events at Six Flags Darien Lake and (at the time) Six Flags Kentucky Kingdom! We used to travel to Louisville for the Arabian horse national competition, and I vividly remember the giant, menacing, inflatable pumpkin on top of the entrance. We never actually went in, and I was FAR too young, but still sticks with me! Darien Lake, on the other hand, was our "home" park (even though we were ~2 1/2 hours away, haha), so we would usually spend a weekend there during the summer and come back at least once for the fall festivities. I was always a costume kid, so we would always attend in costume and usually enter the costume contest, trick or treat, all the fun kiddie fare, haha. Some great memories of feeling the thrill of getting up on the gazebo stage for the first time after seeing performers on it for years and gazing out at the (tens) of guests
I also have a distinct memory of one of the theater shows they put on, which I believe was a loose retelling of the Rocky Horror Show (wild for kids daytime entertainment, lol, but still). I have visual memory of the card board cutout car they used, and the inclusion of Feed My Frankenstein for some reason.
Took a number of years before we ventured to the more spooky offerings, or even stayed past dark, which by that time I had a few more local haunts under the belt. The Ghost Town walkthrough area beyond Superman made a huge impact on me as a kid, some fun set design work there! The biggest unique offering was the Fright Night Field Trip, which involved a bus ride through the camp grounds. They ripped the windows off of the busses and pretty much gave the drivers free reign to punch it down the non-actor areas, and so you really felt the speed (even though we were going, I dunno, maybe 10-15 mph tops). Finally, the Road Rage Cage, an enclosed version of their bumper cars, still impacts to this day how I name my Roller Coaster Tycoon 2 bumper cars, haha.
I also have memories of the local Zoo Boo, which wasn't as scary as it was just a fun spooky atmospheric event. Lots of storytellers, treat stops, but I'll count it as theme park adjacent given the 'established family entertainment venue with an overlay" feel, haha