I’m a big fan of Brookfield Zoo; I love taking the kids to see animals, and it’s big enough you can keep coming back regularly and see new things each time.
Brookfield Zoo will get decently crowded in the summer, but it will never feel as crowded as smaller spaces like Shedd or the Chicago Children’s Museum, and it generally handles crowds better than the Lincoln Park Zoo. If you can go to Brookfield during weekdays in the winter, it sometimes feels like you have the whole place to yourself.
Top Tips
The busiest days are the first few weekends with warm weather in the year, and the first few weekends after school gets out. The zoo handles crowds decently well, but see the crowds page for info on where they will cause problems and how to avoid them.
Avoid the hottest days. The zoo gets packed but animals are inactive or even off exhibit, and my kids' patience and willingness to walk seems to melt with the heat.