Asked about changing nappies William said: "We've done that already," and Kate said "he's done his first nappy already".
The Duke looked at ease holding his son and after speaking to the press for a few minutes.
"We're very emotional," said Kate. "It's such a special time.
Asked how much hair the new prince has, William replied: "He's got way more than me, thank god!"
The Duke and Duchess of Cambridge emerged from St Mary's Hospital with their new baby son tonight to loud cheers from well wishers.
The Duchess said: "It's very emotional, it's such a special time. I think any parent will know what this feeling feels like."
The Duke and Duchess of Cambridge have left hospital with their baby in a car driven by Prince William himself.
The Duke of Cambridge took questions as he stood outside the hospital holding his new son.
"He's got a big pair of lungs on him, that's for sure," said Prince William.
"We're still working on name."