This afternoon, Mrs Johnson was seen paddling on the beach with Dr Biden as Wilfred, one, sat on the shoreline.
Carrie and Boris tied the knot almost two weeks ago at a low-key wedding ceremony at Westminster Cathedral. They then had a small reception at Downing Street.
Wilfred was born in April 2020.
Today, the two leaders and their wives admired the view near the luxury hotel, with Mr Biden saying: “It’s gorgeous.
“I don’t want to go home.”
Mrs Johnson opted for a red mid-length dress, which appeared to be a £325 gown by London-based designer L.K.Bennett, for the walk, while Dr Biden wore a black and white polka-dot dress with a black blazer.
The First Lady’s blazer, which carried the word “love” on the back in studs, appeared to be by French brand Zadig and Voltaire.
After having tea with Mrs Johnson on Thursday afternoon, Dr Biden told reporters: “It’s really nice to be here in Cornwall. It’s my first time. Obviously it’s beautiful for those of you who have been here before.”
She said that she and her husband were looking forward to meeting the Queen as part of their visit, and that the couple hoped to focus on education in their discussions with the royals.
“We’ve looked forward to this for weeks and now it’s finally here. It’s a beautiful beginning,” she added.
As the two men were sitting next to each other in Carbis Bay Hotel, where the G7 summit will be hosted, Mr Biden said: “I told the Prime Minister we have something in common. We both married way above our stations.”
Mr Johnson responded: “I’m not going to dissent on that one. I’m not going to disagree with you there or indeed on anything else, I think highly likely.”
It came ahead of a potentially tricky meeting between the two leaders, with Mr Biden expected to use the meeting to warn Mr Johnson not to let the row over Northern Ireland’s Brexit arrangements put the Good Friday Agreement at risk.