This was sent to me by a friend and I thought I'd pass it along!
I was poking around on the city's website and discovered some good news about the zoo/biopark in the FAQ section. This is particularly nice if you don't have a biopark membership.
"Are there any discounts for kids during the summer? Beginning the Monday after Memorial Day through Labor Day, one full-paying adult can bring in up to four children free on Mondays. This includes combo tickets."