Keeping the focus on the environment, on Thursday, the pair made a visit Greentown Labs, a climate tech start-up, in the city of Somerville, where Prince William issued a warning about the future of the planet, saying: “For all of us, the time is ticking.”
They are also scheduled to visit Roca, a non-profit that focuses on reducing youth violence.
It is the couple's first trip to the US in nearly a decade and their first visit abroad since the death of Queen Elizabeth II.
Their three-day trip to the US has been overshadowed by the growing race row over comments made by the future king's godmother, as the monarchy faces new allegations of racism.
Lady Susan Hussey has resigned from her role in the royal household and apologised after she repeatedly questioned Ngozi Fulani, a prominent black British domestic abuse activist, about where she “really came from” during a Buckingham Palace reception.
Their trip also coincides with the release of the trailer for Prince Harry and his wife Meghan's Netflix docuseries.
The one-minute trailer for the series, released on Friday, featured never-before-seen photographs of the couple, who live in California. In one part of the trailer, Meghan appears to be wiping away tears while Prince Harry sits and tilts his head back, seemingly in distress.
A Kensington Palace spokesman has reiterated comments made before the trip that the Prince and Princess of Wales would not be “distracted” by other things this week and their focus was on meeting communities and local people across Boston before the Earthshot awards.
“My grandmother was one of life's optimists. And so am I,” Prince William said in a statement on Wednesday.
“That is why last year we launched The Earthshot Prize with the ambition to create a truly global platform to inspire home and urgent optimism as we look to save the future of our planet.”
During a lighter moment of the visit, the couple met eight-year-old Henry Dynov-Teixeira, who was dressed as a King's Guardsman.
The boy handed the Princess of Wales a bunch of red roses and said he was “thrilled” to meet the couple in person.
“I am going to scream and tell my best friend that I am now famous,” Henry said.
On Wednesday night, the couple were treated to courtside seats at the Boston Celtics game, where they met Celtics star player Jayson Tatum.
The royal couple and the NBA team also celebrated the achievements of 15-year-old climate activist Ollie Perrault.
Boston Mayor Michelle Wu greeted the royal couple at city hall during a welcoming ceremony on Wednesday afternoon.
Their trip to the US city coincides with one being made by President Joe Biden, who will be in town for a Democratic Senatorial Campaign Committee reception.
The White House said Mr Biden “intends to greet” the royal couple when he is Boston but that details are still being finalised.
The couple on Friday will reveal the five winners of this year's Earthshot Prize and will also visit Harvard's Centre on the Developing Child.
They are also scheduled to tour the JFK Library with Caroline Kennedy, daughter of former president John F Kennedy.
Press Association contributed to this report