Hi--I live in Brevard County. From my door to Disney is about 80 minutes or so. I pass the zoo (at least the exit) on the way out and back when we go.
You could probably get there in 45-60 minutes depending on traffic.
It is a nice zoo--get there early and you can feed the giraffes (They start getting a little full later in the day).
It is free admission for those are are members with an AZA zoo. Otherwise--it may be a little pricey.
They do have playground with slide.
The zoo is broken into the Australian area, Africa, and the americas.
It is a fun time--whether or not it is worth it depends on what your experience with other zoos is and your expectation level. It isn't the San Diego zoo, but it is a nice zoo for its size.
They also have a train ride that the kids love--it costs extra.
You can also go kayaking (minimum age 5) for an extra fee as well.
http://www.brevardzoo.org/
My kids love it there. My favorite exhibit is the otters--especially when you can catch them at feeding time

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ETA: I forgot about the butterfly exhibit--very very very pretty. Though I am looking at there website and don't see it. I wonder if it was just a temporary exhibit

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We are going at the end of the month for a Dinosaur field trip. Supposedly they have set up a dinosaur tour--I believe that is open to anyone . There is an extra fee involved with that.