Unless you live in a rural area, chances are your kids might not ever see many animals outside of a zoo or a circus, apart from pets. These are great places to take your kids to experience animals. If you know someone who lives on a farm, all the better. Consider taking your next family break on one of those farm-stay destinations. Before going to any of these places for the first time, you might like to read books showing the animals they're likely to see there.
Some children are frightened when they first see a massive elephant, etc.
Prepare them and raise their level of expectation by making the animals feel familiar to them. After visiting the zoo, circus, or farm you could find books with these themes and refresh their memory. Have fun making animal noises and reading to your kids. Older children might want to learn more about an unusual or exotic animal. Look for non-fiction books covering specific animals or by country of origin.