When? With kids? I don't recommend the summer as it's hotter than Haiti down here. I've been down here for a long time now and here are a few things to consider.
Food, take your pick as this town has incredible food. Commanders Palace, Couchon's, Any of the Brennan resteraunts, Galatoire's, Emeril's....etc. For breakfeast you can hit the Ruby Slipper, Camilla Grill, or Cafe Dumonde. The list is too long and food and drinks in NOLA are the least of your worries.
You have the D-Day museum, Audobon Zoo, Aquarium, Swamp Tours, Insane fishing (onshore and off). City park has a couple museums and is a pretty gorgeous park if you fee like taking a long street car ride.
Music and nightlife, just plug into any music site and see who is playing when you are down here. Of course this week is the second week of jazz fest so it will dry up for a while after this. You'll still have a ton of choices, but many of the good local bands hit the festival circuit during the summer.