Well the Audubon Zoo has and remains one of my all-time favorite places. In addition to being a top-notch zoo, the grounds are beautiful and there are other landscaping touches . . . Such as a beautiful elephant fountain, the carousel with endangered species animals, and more. The food there is pretty good these days, with a variety (salads, burgers, pizza, chicken strips) offered at the main food site (not too far from main entrance) and gumbo, red beans, etc. offered at the Swamp. The chicken strips are actually excellent, the portion is too large for a single person (at least, to me). The strips are not to be confused w/the nuggets, the usual fast food-type. There is also a very nice gift shop there, and the prices aren’t as bad as you might expect. I can’t remember if there is still a life sized dino exhibit there, or not.
The weather in NOLA is usually pretty nice in Dec, hard to predict of course but usually not really cold yet and often very sunny. Usually a pretty good time to be outdoors.
Also I would recommend the Insectarium, on Canal street. It’s run by the same organization that does the zoo and aquarium, the Audubon Institute. The insectarium is a little small (bugs don’t take up much space) but it’s fascinating. The snack shop has edible bug snacks for the adventurous types, and regular food (just light snacks) for the others. Right now there is also a parakeet exhibit, I think?
And there is the Aquarium, too.
It’s possible that the Audubon Institute might give a discount if you bought tickets to all three venues - Zoo, Insectarium, Aquarium. You could do the Aquarium and the Insectarium on one day (they are both on Canal street). I would set aside an entire day, or nearly, for the Zoo.
There is the Louisiana Children’s Museum, not far from the WWII museum. The 5-year old would LOVE it and the older kids would probably like it too. I haven’t gone in a while but it’s a good facility.
All of these places are very kid-friendly.
Christmas in the Oaks @ City Park is back on track after a few dark years, although the “little houses” as we called them - miniature houses with walkways between, with a whole bunch of holiday decoration type stuff – lollipops, decorative balls, etc., and Alvin and the Chipmunks singing christmas carols . . . All this put up by the Sheriff’s dept — has never returned. 
Too bad b/c my daughter LOVED this at age 3-4-5. But anyway, there are driving tours through the park, and you can park and walk, too. Also, of note, the small amusement area is usually open during the holidays. We just went on Saturday night and it has been spruced up quite a bit. It was kind of a sad little amusement park in the past. It is small but there is a fun slide, a tilt a whirl, a little roller coaster, a small ferris wheel, a train that goes around city park, one of those rides where all sit strapped in and they free-fall you then catch you, a scrambler, and a new ride called the Music Express. It’s just cars in a circle that go around really really fast, and they also rise on one side of the circle and fall on the other side. My daughter and her friend rode it SIX TIMES the other night and it was a great amount of fun just watching them. There are also little-kiddy rides, such as a baby free-fall, little airplane, teacups. Sometimes at Christmas in the Oaks they have stuff like hot chocolate in addition to the usual burgers / hot dogs.
