Mark Zuckerberg and wife Priscilla Chan introduce 2nd baby

Facebook CEO Mark Zuckerberg and his wife are welcoming a new baby, another daughter.

Letter to baby August shares Zuckerberg's hopes for her childhood

On Monday, Facebook CEO Mark Zuckerberg announced the birth of his daughter August on his Facebook page. Zuckerberg posted a picture of himself, August, his wife, Priscilla Chan and August's sister Maxima. (Charles Ommanney/Facebook/Associated Press)

Facebook CEO Mark Zuckerberg and his wife are welcoming a new daughter in a post — where else — on Facebook.

Zuckerberg and Priscilla Chan already have a toddler daughter, Max, born in 2015. They named their second child August.

The couple posted a photo of the family Monday, along with a letter they wrote to August hoping she will get to enjoy her childhood. They write that "childhood is magical" and tell her that she only gets to be a child once "so don't spend it worrying too much about the future."

Chan and Zuckerberg also wrote a letter to Max when she was born, talking about the world they hope to see her grow up in, with advances in science, medicine and access to education.