By Simon Perry

09/03/2012 at 04:05 PM EDT

Prince Harry was “joking and relaxed,” according to an observer, at a charity event in London on Monday – during his first public appearance since photos of him partying naked in Las Vegas surfaced two weeks ago.

After a little boy, Alex Logan, appeared on a British TV news report saying he would tell the prince, “I’m glad you’ve got your clothes on,” Harry, 27, preempted the youngster during their meeting at the WellChild Awards at the Intercontinental Hotel.

“You keep looking up at your Mum. It looks like you’re dying to say something but you’re worried she’ll tell you off,” the prince said, wagging his finger at Logan, 6. “I heard you were on ITV earlier and you said something cheeky but let’s not talk about that here.”

Logan, who has leukemia, was one of the children honored Monday by the charity, which has had Prince Harry as a patron for the last five years.

“He was very calm and composed. You’d never know anything had happened,” another observer said of Harry, who has had the support of the palace since the revealing photos were published. “He was hugging every child.”

At a reception, Harry, often crouching down, spent time talking to the annual event’s littlest guests, including Hope Hillis, 5, who gave the prince two sloppy smooches on the face.

Joked Harry: “But we’ve only just met!”