For a completely free zoo in a public park, High Park Zoo is great! It's a short walk from the Adventure Park. As you walk along the street, you'll start to see the animals' homes on both sides of the little road. They have emus, longhorn cattle, and several other animals kids love. In front of each area, there's a plaque explaining each animal.
My wife and I went on a Wednesday around 7am and happened to meet one of the zookeepers. He was a very friendly man who even let us into the emu cage to pet the large emu. He told us he's worked at the zoo for 25 years and love it.
If you want a free activity for the family, High Park Zoo is recommended!