US President Barack Obama urged young people not to "pull back" from the world and to reject cynicism and xenophobia during a Q&A in London.
Obama's comments came after he faced criticism from leading Brexit campaigners, who branded him an irrelevant "lame duck", over a speech he made supporting the UK's membership of the EU.
President Obama and the First Lady have met Prince George at Kensington Palace.
In pictures released by Kensington Palace, the Prince thanked the US president for his rocking horse, which he received as a present from the White House when he was born in 2013.
The prince was allowed to stay up past his bedtime to meet the US president.
The pictures were taken after President Obama and the First Lady had dinner at Kensington Palace with the Duke and Duchess and Prince Harry, as part of their four-day UK visit.
Barack Obama has warned that Britain's influence on the global stage would be diminished if it votes to leave the EU.
The presidential hopeful says she agrees with Obama comments adding that she 'has always valued a strong UK in a strong EU'.
US president insists that society is "moving in the right direction" in response to transgender student at London meeting.