Maquoketa caves are located in a beautiful park in Iowa. It is a fun place to visit and there is lots of exploring to be done. But make sure that the kids you take are the appropraite age. There are lots of trails and paths to walk along. No strollers are allowed, so you can't go too far with little ones in tow. Great places with lots of fun places for older kids to explore. But not such a great place for little ones who can't walk long distances.
Our entire family has an annual Family Fun Fest and this was one our weekend destinations. The kids (ranging from 6-1 years old) all had a ball. The caves were a ton of fun to explore and we all had a great time. We camped and hiked and got very dirty. The caves were closed this past summer due to a fungus, I believe, so make sure you check into that if you plan to visit there.
There are many caves. A large one that you can walk through that has one coming back to the surface about 1/3 of a mile away from the entrance. Take flash lights, bike helmets, and a change of clothes. Most of the caves are not recommended for inexperienced spelunkers. Our kids, ages 8, 6, 4, and 1 years old, were intrigued by just looking into the entrances of the caves and walking the trails. Consult the website in advance as the caves may be closed due to flooding or controlling a disease that is killing bats.