I go to Halloween Horror Nights at Universal every year (or at least the past 4 years), at least two or three nights each year. The Halloween events are mainly held at USF (nothing really at IOA), and Halloween Horror Nights is a seperatly ticketed event (everyone is kicked out of USF at 5:30pm and the park reopens and transforms at 7pm). HHN lasts until 12a on weeknights and 2am on most weekends. This is definatly a PG-13 (borderline R) event and well worth cost. The park has at least 5 haunted houses, as well as scareactors throughout the entire park, haunted rides, haunted shows, and a great Festival of the Dead Parade. Your 13 year old will love the event and so will the ten year old if and only if he can handle the scariest of horror movies. There are virtually no lights anywhere in the park and fog / loud music everywhere. The scareactors go all out; they will chase you, jump at you, slide on their knees in front of you, and shake trash cans at you. Definatly do not bring the 3 year old. Every year you see well intentioned parents bringing terrified children to the park, and wind up leaving 30 minutes into it. I'm sure if you do a search you can find my last trip reports. Good luck and don't miss it!
Jim
