You may want to consider joining memberships with the NC Zoo or the Aquariums... there are several different levels of membership... You get free (or discounted if noted) admission for a period of 12 months. There are 150 locations across the country that you also have free/discounted membership. Checkout nczoo.com or ncaquariums.com. A family of 4 (2 adults and 2 children) would cost $32 to enter based on ticket prices for the zoo; a family of 4 could buy a tax deductible membership for $59 and have free access to the other zoos/aquariums/centers for 1 year, plus store/program discounts. It's worth considering if you like to take some day trips within the state/surrounding states. Not sure if the zoo does it, but the aquarium gives members discounts on admissions of those that come with them that aren't part of the family that is covered by the membership.
Here are the sites in NC that are included in the membership for free admission for 1year:
NORTH CAROLINA
Nature Science Center of Greensboro/ 50 percent off admission / 336-288-3769
North Carolina Aquarium at Fort Fisher / 910-458-8257
North Carolina Aquarium at Pine Knoll Shores / 252-247-4003
North Carolina Aquarium on Roanoke Island / 252-473-3494
North Carolina Zoological Park, Asheboro / 336-879-7250
Sylvan Heights Waterfowl Park /Scotland Neck / 252-826-3186**
Western N. C. Nature Center, Asheville / 828-299-8522
(If you do the membership thru the zoo, you get 50% discount for the Planetarium in Chapel Hill)