Facebook founder releases photos of his new child.

The Facebook CEO posted the news on Facebook along with a family photo that includes the newborn with her older sister, Max.

Zuckerberg also wrote a letter to August about childhood and "the world we hope she grows up in."

"Childhood is magical. You only get to be a child once, so don't spend it worrying too much about the future," Zuckerberg and Chan wrote in the post. "You've got us for that, and we'll do everything we possibly can to make sure the world is a better place for you and all children in your generation."