Last year, my husband and I decided to purchase an annual membership to Atlanta's kid's museum, Imagine It! Because we are on the road so much, we decided to get the "travel version", which is accepted at museums across the country. This is one of the best investments we have made for our children.
If you've never been, children's museums are a great opportunity to let your child explore in a safe environment. Most of these museums are geared for children no older than twelve, although there are a number of programs for toddlers and elementary school kids. Children can examine things in a hands-on world.
Every museum I have gone to thus far has an art studio of some sort where children can make and do things. This is the biggest hit for my kids. They have enjoyed painting on walls, building sand castles, constructing things from clay, making paper, creating silk screen images, and a variety of other things. The biggest plus for me - no mess to clean up. Pretty much every studio has smocks hanging nearby, so very rarely do you even have a problem with clothes.
Another constant theme seems to be the water room. If you are going to a museum for the first time and it has a water activity, seriously consider taking a change of clothes. You may also want to make this section the last stop on your trip. Kids can build things, race boats, splash around, and just generally get wet. At the same time, they are learning about floating and sinking, currents, and other neat stuff.
One thing I love about the museums is the books. So far, every section I have seen has books of a same theme. For instance, the section on water might have a bunch of boats. If the museum has a toy train table, you can find books on trains and transportation. You are apt to find comfy chairs and beanbags near these books, so your kids can settle down and read.
The biggest downside comes if you have multiple small children. I have four kids under the age of six, and we make sure we discuss the fact that we will all stay together. Thankfully, the youngest is a newborn, so I don't have to worry about her running off! But there have been tense moments when one of my kids would wander away, and I'd have to gather up three to go in search of the fourth. Just make sure you lay down the law before you go in - and maybe take both parents on occasion - and you should be fine.
These museums can be somewhat pricy, so I would suggest a family pass. Usually, you can visit once to try it out. If your kids enjoy it - and I bet they will - you can then include the cost of that ticket in your annual membership. Just make sure you visit enough to make the cost worth it!