Aloha, Alyse!
Welcome to the Disney Parks Moms Panel. I'm so excited you are planning to visit the Disneyland Resort this January! This is one of my favorite times of the year to vacation at the Happiest Place on Earth, because I love the cooler temperatures and lighter crowds. I highly recommend bringing layers and storing them in a
convenient locker rental during the day so you prepared for chilly evenings.
When the holiday festivities come to a close on January 6, 2019, the Disneyland Resort will be transformed to its classic, magical self. During this transformation, some attractions that were decked out for the holiday season will be closed for refurbishment. You can always check the
Daily Events Schedule online usually up to 6 weeks in advance to see which attractions, restaurants, or entertainment offerings will be closed for refurbishment in both Disneyland Park and Disney California Adventure Park during your trip. Looking at the schedule it appears that the last day of refurbishment for Haunted Mansion is January 17, 2019. This means that you should be able to experience the 999 happy haunts of this frightfully fun attraction starting on January 18, 2019. Typically in the past, "it's a small world" Holiday was available for Guests longer than Haunted Mansion Holiday and therefore has a later refurbishment date to restore the original attraction. Usually this happens at the end of January into early February, so it's a possibility that you may still get to experience "it's a small world" Holiday and the original Haunted Mansion at the same time during a brief window when you visit. Keep an eye on the schedules in the next couple of weeks to verify these refurbishment dates.
I hope this helps, and please return if you have any other questions. Have a magical day!
-Jennifer