Mark Zuckerberg has announced the birth of his second child with Priscilla Chan – a baby girl named August – in a new letter published on August 28.

The Facebook’s co-founder has urged his young daughter to play outside and enjoy the wonders of being a kid, in the heartfelt letter posted on his social media site.

In the gushing missive, Mark Zuckerberg and Pricilla Chan speak about the magic of childhood and the importance of play.

He wrote on his Facebook page: “Priscilla and I are so happy to welcome our daughter August! We wrote her a letter about the world we hope she grows up in, and also hoping she doesn’t grow up too fast.”

The couple posted a similar letter to daughter Max in 2015.

Image source Facebook

The post, which appears alongside a family photo on Mark Zuckerberg’s Facebook page, encourages the new baby not to “grow up too fast”.

“The world can be a serious place. That’s why it’s important to make time to go outside and play,” said the letter, signed “Mom and Dad”.

The call to discover a childhood outdoors is at odds with the aims of Mark Zuckerberg’s social media empire.

“I hope you run as many laps around our living room and yard as you want. And then I hope you take a lot of naps,” the parents wrote.

“Childhood is magical. You only get to be a child once, so don’t spend it worrying too much about the future,” they added.

It marks a lighter tone from the open letter written to welcome baby daughter Max, which reflected on the problems facing younger generations and how technological progress will drive change.

At that time, Mark Zuckerberg and Priscilla Chan said they would donate their fortune to the Chan Zuckerberg Initiative to make the world a better place for Max to grow up in.

The organization has pledged billions of dollars to improve life for their children’s generation with goals such as eliminating disease.

However, the parents wanted to shield their latest addition from these kinds of concerns, telling their daughter not to worry about the future, adding: “You’ve got us for that.”

“You will be busy when you’re older, so I hope you take time to smell all the flowers and put all the leaves you want in your bucket now,” Mark Zuckerberg and Pricilla Chan said.