We took a trip to the zoo a little before Matthew was born.  It was kind of like the last trip with just the girls.  We went in the afternoon and avoided the crowds and spent a couple hours walking around and watching the animals.
The great thing about Chiba zoo is that you can get quite close to the animals and there is enough variety to keep the children entertained.

The giraffe`s head is just a few feet away as I took this picture of it eating grass by the fence
The girls are just a couple feet away from the giraffe.  You can see their shoes, the red ones
They don`t have the more agressive animals like the rhino or hippopotamus, or predatorss like tigers or lions though, but the usual big guys are there: elephants, giraffes, gorillas, and the like.
Ultimately the zoo reminds my children that the animals in their books are real.  In suburban Japan there is not a lot of exposure to wild animals, so the only thing you have are the pictures on the ABC charts and in books. 
It was fun and only took a couple hours to see most of everything.