The actress, who recently starred in the comedy What To Expect When You're Expecting, announced on her website the arrival of Magnus Mitchell Handelman, who was born via a surrogate.
The new baby joins his older brother, 20-month-old Felix, who was also born via a surrogate after the 38-year-old star of The Hunger Games and her producer husband Max Handelman faced infertility issues.
The new mother said: "I now turn my attention to managing two boys under two. For which I am thankful. And all their poop. For which I am less thankful."