M.R.
Go to the aquaium and the zoo and the insectarium! Walking in the quarter is fun, but know that they may see some things in windows that some people find disturbing, but they are not so bad that it keeps children away for the most part. My daughter took field trips down there so the locals go all the time. Take a ride on the Ferry, kids love it, and if you walk on, it is free. On the Westbank there is the Mardi Gras museum, which is a great tour.There are many other museums, the DDay is good, but might not interest little kids, and there is a great children's museum too. Take them on a Mule buggy ride! These guys are full of information about the city.
Have a blast-be sure to go to Cafe Du Monde!
M.