This is owned by Purina, the large pet food company. It's an area with many domestic animals and they often have major dog competitions here as well. They have obedience shows, grooming demonstrations, hands-on petting of dogs and cats for the kids, and you can even milk a cow.
I believe that admission is free but don't quote me on that. You'll have to check.
Purina Farms is about 25 miles west of the 270/44 interchange in St. Louis, so plan for that travel time.