I was going to mention the same thing. Zoo Lights at the zoo, it's Friday and Saturday nights, but I think started the 13th it is every night thru xmas eve. Check their website. Very pretty, for kids and adults alike. I go every year and I'm not a kid!

They do have a ton of activities for the kids though.
It's no where near I-40, but 40 goes around town, not through it. I take it you do not know where you are staying in Memphis? If you are coming from Cali (west) you'll hit downtown first. What day are you coming? There is an xmas parade downtown...on....maybe the 15th? Not sure. The zoo is between North Parkway and Poplar, near McLean. (Overton Park, if you look at a map). Really, really easy to get to.