I am really happy for you and your grandchildren...NCV are great, and I think your grandchildren will have a blast. They have 3 pools in the main area, and two others located in other areas of the resort. They have a special teen club next to the main pools, and ideally it would be nice to stay close to that area. Hopefully you will have a car, so you can get over to Newport Beach/Balboa Penninsula, for miles of beach, surf, a cool boardwalk. Park on Balboa Penninsula down near the pier, and the are shops whee you can rent surf boards, boogie boards, bikes, roller blades, etc. There are also restaurants, and if you walk over to the fun zone, by the marina and ferris wheel, then you will find boat rides, boat rentals, jet ski rentals, etc. You all will have a wondful time!
For shopping, Fashin Island is a short drive away, and Laguna beach is south,
Which is fun, too. And, Crystal Cove is just down the hill. The Marriott has shuttles that you can ride for free to Crystal Cove, Fashion Island, and Laguna. Balboa and Newport just happen to be our favorites.
If you like to golf, Pelican Hill's course is a fun time, too. Four days will go fast, so enjoy!