Lincoln Park is a small zoo that you can cover without breaking a sweat. Brookfield is much larger and more commercial. It has fun rubber- wheeled trains that you can ride around so you don't tire yourself out if you don't feel like doing a lot of walking.
Of course this place is not free either, like Lincoln Park. It is still worth the cost of admission; you and your kids will enjoy spending a couple of happy hours here on some sunny summer afternoon. Or for a real adventure, go in cold weather. It is open year round.
It is your classic zoo experience. For some reason, as I am remembering it now, I am thinking of the giraffes with their long tongues, grabbing forbidden snacks.
http://www.brookfieldzoo.org/
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