My 4 year old has great ideas. She found a rope in the backyard and started linking it between different things in the yard to create a "zoo". The zoo has created a few hours of entertainment because we take turns being different animals in the cage, a zookeeper, or a visitor to the zoo. Plus it can be reconfigured at any time. This is the set-up yesterday. Today we moved the ropes around and made it have more "cages".
Here are my baby pony and my baby zebra. You can tell which is which because the zebras like popsicles...well, at least they do at our zoo!