As Kaylee said,it really depends on the individual kids.We went in October 2001 & 2002.The first time mine were 11,14 & 16,then obviously 12,15 & 17.
The eldest two said it was their favourite thing on the whole holiday both times.It is an amazing night.
My youngest was scared of the scareactors and even when he was genuinely scared and screaming,as Kaylee said, they didn't back off and leave him alone.I thought surely they can tell the difference between a kid screaming and being scared and an adult/teenager screaming and loving it! Luckily the first time I was on a VIP tour,and when Mattie refused to go in a maze,we went in and left him with the tour guide.When we came out we were amazed as he had gone in with her afterwards.What she had done is call a scareactor over in to a quiet area,ask him to show DS his face under his mask and that he was a 'normal' person.after that he was away and never looked back,and although screamed and was scared it was in a good scared.
Shrek36D, you will know best how your kids will be.Just tell them before you go and constantly remind them that there are people under the costumes and they are acting! If they are up for it they will love it even at their youngish ages!
Piemanxi,I would have concerns anout taking a child your child's age.It was much more crowded last year at IOA, I did see some toddlers in pushchairs there but it was far more manic and I saw more rowdiness.Do you have someone you could leave your child with?