Getting out to see animals in the fur is always an exciting field trip for kids. They may have already done it several times in their lives, but it never gets tiring and there is always something new to learn. Before going, ask if any children have been to similar places, what they thought of them, and what they learned.
Almost everyone loves a trip to the zoo. Before you take your students, get a list of all the animals you will see. Ask the students what they know about these animals. You can either do it as a class or have the students write down what they know individually. With older students, have them bring a notebook to the zoo and write down two or three facts or observations about each animal they see. Test their knowledge again after you return. Are there certain animals that everyone learned a lot about? Were any animals somewhat unmemorable? Why do they think that is?
Make sure that whatever wildlife you plan on visiting, the children are aware that they should never try to touch a wild animal. Remind them that even domesticated pets and farm animals should never be approached or touched without adult supervision. Even if an animal looks calm and kind, you can never predict if it will get scared of you and bite.
Your students can learn all about local wildlife up-close and personal at a wildlife refuge or rehabilitation center. Make sure you research what animals will be there before you go so you know what you are looking for. Except for injured animals, which are kept in special enclosures so people can help them heal, the animals run free like in nature, not like a zoo. Since it's more difficult to actually see an animal in its natural habitat, make the field trip a scavenger hunt. Make a list (maybe with simple drawings) of the wildlife that live at the refuge. Give your students a copy and have them check off animals as they see them. When you return to the classroom, find out if there are any animals that no one saw. Why do they think no one saw it? Is it nocturnal? Does it hide during the day? Are there very few of them? What other reasons might there be?