Do I have to pay for my 2 month old baby and what days is the zoo free?

I don't think there is any day when it's free. 2 years & under it's free. For $210 a Family Zoos Plus Membership gives you unlimited access to the Bronx Zoo, Central Park Zoo, Queens Zoo, and Prospect Park Zoo for one year for 2 adults, up to 4 children, and a guest for one year

Can you pay at the gate

The Bronx zoo is free on wednesdays...

It's free for kids under 3 years old and no free days