Hi, Christa!
Welcome to the Disney Parks Moms Panel. Wow, your pixie-dusted vacation is just around the corner! I hope you and your little one are getting excited for all the magic that awaits you!
While both theme parks have holiday-themed decor, attractions and entertainment to enjoy, I recommend that you visit Disneyland Park on the first day of your trip. January 7 is the last day for your son to experience the Haunted Mansion Holiday attraction,
A Christmas Fantasy Parade, and the "Believe...In Holiday Magic" Fireworks Spectacular. After the fireworks, snow will fall in the skies above “it’s a small world” Holiday in Fantasyland, over portions of Main Street, U.S.A., and near the Rivers of America as a special seasonal treat. Although it’s not a holiday-themed attraction, Dumbo the Flying Elephant is also slated to close January 8 for refurbishment, so that may be another reason to visit Disneyland Park first.
The exception to this advice is if your son is a big fan of the movie Cars (like my son was at 3 years old!), in which case you may want to experience
Mater’s Jingle Jamboree and
Luigi's Joy to the Whirl, two Cars Land attractions that are decked out for the holiday season. It’s also worth noting that some attractions at Disney California Adventure Park, including California Screamin’ and Mickey’s Fun Wheel, are expected to close January 8 while the Paradise Pier area is re-imagined, so it would be your last chance to experience those.
I hope this helps you, Christa. Please feel free to write back with more questions!
Wishing you magic,
Courtney