The 36-year-old actress adopted son Jackson recently and confirmed the news on Wednesday.
She told Ryan Seacrest on his Los Angeles radio show she has been overwhelmed with love and support since sharing her baby joy.
"It's been amazing, the amount of emails and congratulations," she told the American Idol host.
"Everyone's just been so lovely, so it's been really nice."
Theron also says she is getting to grips with motherhood and has adopted a nifty trick used by many parents.
"I didn't think I would be a fan of the swaddling," the Oscar winner said.
"But the swaddling is pretty amazing. It looks a bit like a straitjacket, but for some reason they just love it."
A source close to the actress told Us Weekly that the baby boy is now four months old and was born in the United States.
This is the first child for the South African-born star. She is single following her split from Stuart Townsend in 2010 after a nine-year relationship.
However, Theron won't be bringing up baby Jackson on her own and will rely on family members for support.
"Charlize's mom [Gerda] has been helping out with the baby," a source told People magazine.
"She seems so happy and will be a great mom."
Theron will next be seen starring as the evil queen in Snow White and the Huntsman.
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