(Photo credit: Max Mumby/Indigo/Getty Images)

These days, Prince William and Kate Middleton are spending all their time with their newborn son, but when it's time for their first night away from the baby, Prince Harry joked that they're going to need to write a pretty big check.

"It's fantastic to have another addition to the family," Harry, 27, said today at an event for his charity, Sentebale. "I only hope my brother knows how expensive my babysitting charges are."

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Will and Kate, both 31, welcomed George Alexander Louis on Monday and, since then, the new family has gone to Bucklebury to stay near Middleton's parents.

"He's about that long and about that wide," joked Harry when asked about his impression of his nephew. "When I saw him, he was crying his eyes out like all babies do, I suppose."

Photos: Will and Kate Show Off Baby George

Upon introducing baby George to the public, in fact, Prince William said, "He's got a good pair of lungs. That's for sure!"

Though Harry wasn't sure who in the family the baby seems to take after - "He's about four days old, so I think you can judge that one by yourself. I have no idea," he said - he's certain about what his role in his nephew's life will be.

"To be sure he has a good upbringing, keep him out of harm's way - and make sure he has fun," Harry said. "The rest of it I leave to the parents."

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