SeaWorld in San Diego is a wonderful aquarium/park to take the family, especially on a nice summer day. It can get hot, but there are the shows where you can sit up close and get wet to cool down! The shows are very good, and probably one of my personal favorites for visiting. But kids like to walk around and look at all the different animals, from the seals to the dolphins and of course the famous Shamu orcas. It can be pricey, as all theme parks are, but Sea World is overall a nice all-day outing for families that enjoy animals.

Knott's Berry Farm is a pretty nice amusement park to visit if Disneyland is too expensive. It does have more intense roller coasters though, which are probably suitable only for older and "braver" children. But there are areas/things for very young kids to enjoy as well, such as Camp Snoopy. It is a nice park to walk around and is not as crowded as Disneyland. Nonetheless, like all amusement parks, you'll spend a "premium" on food/drinks/souvenirs here.

The Henry Doorly Zoo is very large and filled with many animal exhibits and things to see. It is definitely an all-day sort of place to visit, and you'll spend a lot of time walking around and viewing all of the animals. It's a great place to take kids who love animals, and is much larger than many of the zoos in the surrounding area. The set-up of the zoo is very attractive, and it's definitely a nice place to spend a day.

The Nelson-Atkins Art Museum in Kansas City is a nice museum to visit with the family, especially if you have members who enjoy art/cultural artifacts. Of course, like with most museums, young kids may become tired or bored, so it does depend on your individual interests. The building is very beautiful though, and there are places to walk around outside as well as rest. There is a cafe where you can buy some snacks/food, or you can pack your own and find a place to rest/eat. The Nelson-Atkins museum is definitely worth checking out.

Union Station is a nice building to visit. It houses several exhibits that change every so often. The building itself is free to enter, and it's architecture is expansive and nice to observe. But if you want to view the exhibit(s), you'll have to purchase tickets, which can get pretty expensive. I'd suggest visiting if there is an exhibit that is a definite interest for members of your family (we went to the Body exhibit a while ago), but otherwise maybe waiting until there is an exhibit of interest to go to Union Station.