As much as Hermann has to offer adults and couples you will have to venture out to entertain kids.  That's alright, nothings that far.  Six Flags is about an hour away and Jefferson City and St. Louis can be reached by a short train ride.  Not to mention the Katy Trail, Meranec River, and Lake of The Ozarks.

Six Flags, as you know, is the fun filled amusement park featuring the Screaming Eagle and Bugs Bunny.  From Hermann you just head up Hwy 100 to I-44 where you will only have about 15 miles to Six Flags.  While you are out that way you can check out Purina Farms, Shaw Nature Reserve and Historic Washington MO. Amtrak visits Hermann twice a day going both directions.  East takes you to Washington and St. Louis, while the other takes you West to Jefferson City and onward.  Not only is the train an inexpensive, fun way to travel, but it is very "green" using less energy than a car to carry dozens of people.  The Katy Trail is a 250 mile rails to trails line that passes Hermann right along the Missouri River.  The Meramec River is a popular floating river and everyone knows the Lake of The Ozarks!

Check all of the above links, as well as these tourism links to plan your trip.
www.visitmo.com/
www.missouribeautiful.com/central-missouri-tourism/
www.missouriwinecountry.com/
www.hermannmo.com
www.hermannwinetrail.com/