If you can get a "front of the line pass" at the amusement park - get it. It's generally worth the money especially as you've come so far.
Make sure the rental car has SUNPASS for the toll roads. Roads are good, but nothing is more stressful than digging for change with excited kids in the car and some meanie behind you honking.
For 3 and 5, Legoland would be awesome! A hotel with a kid-sized pool is worth the premium. Don't forget sunscreen. Even in winter.
Don't wear ridiculous huge white leather high-top tennis shoes - they'll think you're from the United States.
angela