I like that you're budgeting 2 days. People often sell this park short, but know that your 2 days will be leisurely, as the lines aren't long, and there's not as much to do here as at WDW. First of all, what time of year are you going? There are times of the year when the park closes for one or two days a week, and the water park is closed a good chunk of the year, so consult the calendar on their website before you book. Second, there are times of year when they have special events that include extended hours and fireworks at night, like every weekend this summer, weekends around Halloween, and weekends around Christmastime. Again check the calendar, check to see if your trip is going to be at one of these times, and schedule your
Legoland stay for the weekend to take advantage of the extras, which are fun. They give you special glasses that make the fireworks look like exploding
Lego bricks.
Generally, for your park day, start from the back of the park and move to the front. The Driving, Boating, and Flying schools tend be the most popular, and they are at the back. First thing in the morning, sign the oldest up for a Mindstorm class. If your kids like the Lego Movie, go see the new 4D show they have (use the times guide)-- super cute-- and meet Emmet and/or Wyldstyle right after. There's play areas all over the place with giant Lego bricks. We can't get past one without DS needing at least half an hour to play; that's why it's good that you're budgeting adequate time to enjoy the park. The play areas are really enjoyable.
We liked the water park, too. It's small, but there's lots of things for kids of all ages in one area. In the main slide structure, the higher you go, the more advanced the slide (nothing is really intense, though), so kids can individually figure out their limits and stay where they are comfortable. Do take advantage of the lazy river; there's a surprise with the giant Lego bricks there.
My last suggestion is about food. It is universally bad in the park. We usually bring Publix subs in with us. There's a Perkins across the street; don't be afraid to leave the park to eat. Apple fries are worth a try, but even they are overrated.