Hello - we took our 5-yr old in Nov 99 (birthday in March, so 5-and-a half). He loved Quest and we went 2x in the week we were there. The Hercules video game was great; the raft-ride experience was great and he enjoyed the video games he was familiar with. He even enjoyed the older video games and figured out how to play Dig Dug right off the bat. He wasn't tall enough for the Buzz Lightyear bumper car attraction; but he watched from above. The Cheesecake Factory was also a big hit, as it was a familiar name to him.
If you have a LOS pass by all means go. But if you're going to pay full price for the tickets I would think twice, esp. if your kids aren't familiar with that many video games. It really is a great place. Hope this helps! (BTW, where do you live in LA? We lived in Lakewood before we moved to LV)