Credit: Flynet

Baby's first Christmas!

Sandra Bullock and little boy Louis Bardo -- he turns one next month -- got into the holiday spirit over the weekend.

Single mom Bullock, 46, helped her adopted son celebrate his very first Christmas season, arriving at a yuletide bash of a friend in Tujunga, Calif. Saturday. See more pics of Sandra and Louis at the holiday fete.

"Sandra was in a great mood," a witness tells During the low-key bash, little Louis took a pony ride, donned a Santa hat, and even sat on Santa Claus' lap.

"Everyone was commenting on what a sweet and mellow baby he is," the observer marvels. "It looked like they had a great time!"