When introducing children to nature the key is to take it slow and let their curiosity guide the way.
Left to themselves, children find ants to be fascinating to watch: an ant struggles to drag a piece of food larger than itself, two ants from the same hill touch antennae in recognition when they meet, a parade of ants follow an invisible scent trail...but introduce an adult into the event and ideas change: "Don't touch that ant, it might bite you!"or "Don't leave your sucker there, it will draw ants." Suddenly that same fascinating ant becomes something bad.
Children accept what they experience at face value. Adults bring along a lifetime of prejudices through which they filter what they see: prior experiences, the attitudes of parents and others or stories they've been told.
Children question what they see. "How can it do that?" "What are they doing?" "How do they know where to go?" The input they receive from an adult is paramount in shaping their attitudes.
Encourage children--or better yet, join them--to watch for the answers. Be aware of messages you send. Don't respond with "Time to go," "We'll be late," or "Wash up for supper." Translated, that means "Ants aren't important. We have better things to do." To a child, "Don't touch that ant, it might bite you" may mean "Be afraid. Nature isn't a safe place to be" and maybe even "Small animals are yucky/scary/bad."
Without negative messages, children need only opportunity.
Watching an ant try to climb the steep wall of a sand castle, presenting it with new challenges like a stick it could climb, and the bustle of activity around an anthill if a crust of bread was left nearby were once experiences spawned by free time--being outdoors without a goal. In today's world, children often lack unstructured time in the backyard. Without it, they lose intimacy with Nature.
Responding to "I'm bored" by saying "go watch an ant colony" probably won't be well-received, but given enough quiet time, it will happen. Somehow, children will discover an ant colony when they're ready to learn about ants, given the exposure.
To share Nature with a child, try being the one to ask the first question. "Where do you think those ants are going?" Set the stage and then get out of the way. If the time is right, the seed is sown. If not, move on and try again another day. Or take a meandering walk. Point out a bee visiting clover; turn over a rock to see what's underneath.
Allow some silence. Let the child be the guide. Follow his lead. Don't push. Don't set goals. The trick is to go slow enough to give him the opportunity to see something.
Hopefully, you won't make it across the yard.