I was invited to a White House reception last year in honour of Black History Month; I had worked on Capitol Hill for 10 years. I was allowed to bring a guest, so I took my three-year-old son, Clark. He knew the significance; he knows who Barack Obama is. His favourite book is our White House Pop-Up Book.

Clark was one of the youngest people there; he’s very personable and loves interacting, so as soon as we arrived he took off, making his way through the crowds with me trying to follow. We hadn’t been there long when an usher spotted him and brought him to the podium where the president was due to speak. He stood near the front while the usher prepared the stage, looking at the crowds, completely unflustered.

When the president came out, Clark made his way to the front of the rope barrier. I couldn’t get through the crowds myself; I’m not the lady standing behind him, I’m just to the left, barely in shot. I don’t know who she is, but Clark was completely unfazed.

After he’d spoken, the president and first lady greeted the guests. When he reached Clark, Obama knelt down, straightened Clark’s tie, and talked to him for about a minute. I couldn’t hear what they said. By the time Michelle reached us, I was standing back behind Clark. She asked how he was feeling, checked he felt safe and not too squeezed, and we took a selfie. Half an hour later, Obama signed Clark’s book: “To Clark – dream big dreams!” He didn’t want to leave – he wanted to look in all the rooms, and soak it up.

Later that night, a friend called to tell me that this photograph was on Instagram, which I don’t use. I was taken aback, it’s such a beautiful picture. It says: this is my president, and I can be whatever I want to be.

Two days later, I got a call from the official White House photographer, Pete Souza. He wanted to talk about the picture, because it had such an impact: a young African American boy with our first African American president. He sent us a copy plus two outtakes, and Obama signed it: “Clark – thanks for visiting the White House. Dream big dreams, and work hard to achieve them – you will do great things!”

A canvas of the photograph hangs in Clark’s room; a month ago, it appeared on the president’s website. Kids and teachers at his school say, “You’re famous!”, but I think he’s a bit too young to realise.

The Washington Post asked me if I thought Clark realised he was talking to a black president. I don’t think children see in colour – and he’s the only president Clark knows. He calls his white friends “brother”. We’re exposing him to politics: we read him stories about how the world works, and listen to the Hamilton soundtrack in the car. We’re going again to the new National Museum of African American History & Culture in Washington DC.

I’m hopeful Clark will see another black president in his lifetime; the next generation of leaders are already coming through: Harold Ford Jr, Senator Cory Booker, new California senator Kamala Harris. Clark knows he has to work hard, but he has an exciting future ahead of him.

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