They do allow kids in, but not too young. They sell shots of something as you walk thru Margaritaville area to get back to the rides. Most of the rides are open. They also have fog machines running and employees dressed up really GOOD! They don't jump out at you or touch you, they just walk right up to you quickly out of the fog. There were alot of young people there the night we went - lots of girls screaming and giggling. It is startling but fun! There are a couple of haunted houses. I didn't go in those but my kids did (ages 12 & 15).
The only thing I was disappointed in was the ticket prices of the Halloween Nights. They were promoting a special ticket price on-line but the tickets were much cheaper when we got there! Once you get inside the park, you can purchase the tickets for the night you want to attend.
The time passed very quickly while we were there. There were so many people and at times it could be hard to see for the fog that it took us quite awhile to work our way around the whole park. We were there until closing, even though we did not intend to be!
Security was tighter during the Halloween Night than during the day. I took a backpack (instead of purse) with a bottle of water and they made me practically empty the backpack for inspection and I was asked to throw the water out by emptying the bottle into a garbage can (they watched me pour it out). I didn't mind, as they were nice about it, but be prepared.