Hi, Eiliana!
Early December can be a great time to visit the Disneyland Resort because the entertainment schedule is in full swing and holiday decorations have been added around the resort, but crowd levels aren't nearly as heavy as the week of Christmas Day. The holiday decor is gradually installed when the parks are closed and is complete by mid-November, when the holiday season offerings officially begin. So yes, you will be able to enjoy all the Christmas decorations, special treats and entertainment during your visit!
Your family won’t want to miss the Haunted Mansion Holiday and “it’s a small world” Holiday attractions, and the "Believe...In Holiday Magic" fireworks show’s finale of snowfall on Main Street, U.S.A. is a must-see. On the “Holiday Time at Disneyland” Tour, Guests can hear holiday tales from Disneyland Park history, experience seasonal attractions and watch “A Christmas Fantasy Parade” from a reserved viewing area while enjoying a delicious treat and warm beverage. Please call (714) 781-TOUR (8687) to reserve spots up to one month in advance.
I hope this helps, Eiliana, and that you enjoy a perfectly pixie-dusted holiday season visit to the Disneyland Resort! Please write back with any other questions you may have as your planning continues.
Wishing you magic,
Courtney