No you don't
Not sure either. Generally you don't. Just say it to them. But my wife gave them 3 City pass, instead of 2, and they took one more pass without hesitation.
No you don't need a birth certificate for proof of age. If they ask you just say the child is under 3. Couple of years ago we had the season pass and my son was under 3 and they never said anything. Have fun!
I am not for sure but it was amazing it was my first time going enjoyed it whit the first lady my daughter Jada her class went on a field trip
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