So much fun! There are lots of amazing shows, some of which you will get wet at, especially if you sit in the front. It is a nice variety, though, with many kinds of sea animals of different sizes. Please bring sunscreen and/or hats for your kids. I saw too many very small children sitting in the sun for long (30-60 minute) shows. Shade is not always an option, so please be prepared and keep them hydrated as well.

We got a guide. It cost a little extra, but you're guaranteed to see a lot. They put on shows in the different villages, and it's hard to time them if you don't know your way around. Going with a guide means that you'll see the shows.
If you don't go with a guide, you can take your time and do different crafts and classes within the different villages. You may not see many shows, though. When the luau starts in the evening, the rest of the place closes down shop.
The luau is entertaining and good food, but it's not very authentic. They narrate a description of how what they do relates traditionally, but they don't really walk the walk. The evening show is similar, in that it is beautiful but not very authentic.

When we went, we didn't have kids with us, so I don't know first hand about the kids club another activities specifically for kids. It was a beautiful resort, though. It has lots of plants and water features. It has penguins that live right there, birds that the handlers will let kids feed and touch, and many beautiful photo opportunities. We weren't impressed with the dining choices on site at the time, but within walking distance, there are lots of options. We preferred a hotel down the beach for a wonderful breakfast buffet including lots of fresh fruit and pastries. It was a lovely walk in the morning too.
One thing I don't recommend is their spa. We each got a massage, and they were not good and WAY overpriced.
Also, get familliar with the on-sight ABC store. It has everything you need for your stay and souvenirs at reasonable prices.

The Sunset Zoo is a pretty small zoo, but it's on the side of a hill, so going involves lots of walking and a good workout for your calves, especially if you're pushing a stroller.
It is pretty inexpensive, so don't hesitate to save money. Just be prepared to walk and bring your camera to capture a picture of the free-range peacocks.

I was raised near the Cosmosphere and didn't know what a blessing it was. I loved seeing the IMAX films. The IMAX theater at the Cosmosphere is different than other IMAX theaters, though. It wraps around the audience to give a much more realistic, almost 3-D experience. My grandparents were convinced their chairs had moved when they went. It is absolutely amazing, and for the price of a regular movie, you won't be disappointed. Be aware that if you have to leave, you will not be allowed back in, so take turns if you have really small children or won't be able to sit for the whole show.
The rest of the Cosmosphere is great too, so plan to spend most of a day there if you can.