We went two years ago, kids were 4 and 11. We took my little sister too, who was 13. They all had a blast. The little one still remembers some of it, but we plan to go back when she is around 8, and the oldest will be 15. All their ages had things to do.
They have strollers you can rent at each park too, for $10 a day (they give you a ticket in case you go to another park and then you get a free stroller sicne you paid the $10 at another park that day). We got these for when the little one got a bit tired of walking - this stopped her from getting too tired and grumpy. They have stroller parking at every ride. I didn't leave my belongings in the stroller, though, because I don't trust people!
Luckily, because I had no diaper bag, we were packed real light and it was no biggie to grab the one little bag and be off to the ride.
It seemed that those parents with kids who couldn't walk and weren't potty trained and had to have bottles were miserable by late morning/early afternoon.