Sounds like a good idea, might bring more people to the zoo if they have to pay less overall if they bring kids.
If you have a bunch of kids, it can quickly become an expensive day out. I think making kids free is a great idea.
Free entry for kids is a really good idea, I think it would greatly increase the number of people coming through the gates, as I think a lot of families find the zoo is too expensive following the increase in admission fee. Add on the cost of lunch and souvenirs and it becomes an expensive day out. As a member, I don't have to worry about prices too much, but I can see how it must be off-putting.
Great idea. I just took my kids to Healesville for free. As well as my admission cost, I ended up spending more than I usually would on food and stuff from the gift shop because I felt like I was getting such a good deal. In fact, I almost felt like I owed them Lots of other families there doing the same.