Actress Sandra Bullock and comedienne Chelsea Handler helped Charlize Theron celebrate her son's first birthday a second time with a party at her Hollywood home on Sunday (17Feb13).

Theron had previously treated little Jackson to a superhero-themed bash in January (13), with guests including Jason Bateman and Marley Shelton, and she decided to throw him another gathering this weekend.

A source tells, "(It) was a low-key, mellow birthday party with only a few close friends and family. The kids were running around the yard while the adults sat and chatted. Jackson was practising walking the whole time and was very happy and active...

"At the end of the party there was a birthday cake and everyone sang to Jackson."

The little lad sure was spoiled on his big day - Bullock and her adopted son, two-year-old Louis, arrived with a huge bag of presents from Landis Labyrinth Toy Show.

Theron adopted the tot last March (12).