Virginia Beach isn't worth paying for, but it might be worth it to go for free. I have lived there several times since 1997 and now that I am out of the military, I will never go back voluntarily. There just really isn't all that much to do.
The beach itself is nothing much. Ohhhh, its water and sand. there is a boardwalk with overpriced junk being sold. Its nice to walk it or bike it, I guess, but don't expect anything you can't get anywhere else up and down the east coast. I have heard during soft shell crab season, (now-ish?) its one of the best places to get that, but i'm allergic to shellfish, so I never tried it.
Entertainment - well, everything that I could even think of has been mentioned. If you need an indoor day, Lynnhaven Mall isn't the worst place to go if its raining out. Its not too far from the beach.
Food - I mentioned the crabs, but not sure if my memory is right as to the time of year. If I were to go back, which I hope I never do, I would make a point to go to two places. both a few miles up Virginia Beach Boulevard on the right. One place is called Duck Donuts. You special order them at the counter and they make them in front of you. Doesn't get more fresh than that, and they have good options, and really taste awesome. You likely only need one per person, but if you are a fatass, you could put down two. I would definitely go to Wing King. Its a little farther up va beach blvd next to the burger king. Great wings. Probably the best I've ever had with a decent selection of beers and not too expensive. There is a batting cage right behind it, but 4 might be a little young for that.
There are air shows in the area from time to time. You can look it up and see if there is an air show the time you will be there. Oceana is really close and kids always love air shows (bring hearing protection), but it would be pure coincidence to be going on while you are there. If you do have the chance, though, its likely worth the trip by itself.
If I think of anything else, I will update. I really hated living there, but it was more because of the extreme population of military and ex-military, bad traffic patterns and lots of young drivers as a recipe for annoyance.