L.L.
Hi S.!
You do not have to purchase the Sesame Street exhibit. If there are 3 of you going, you'll pay $14 with your coupon. If you want the exhibit it would be an extra $12! I've been several times with my 2 year old and we have a membershib so the exhibit is free. It is worth it to go up for when it's included in the membership, but I don't think it would be worth an extra $12 to go up there. It's on the top floor, so your kids wouldn't even know its there if you don't want to pay the extra.
I hope that helps! Let me know if you have any other questions!