Biden, a longtime teacher, and the Duchess of Cambridge participated in the roundtable with several British early education experts and remotely with a handful of specialists from the United States.
It marked the first meeting between the current United States' first family and the British royal family and took place during the first day of the G7 Summit being held in Cornwall.
The duchess said it was "a huge honor" to welcome Biden to Britain.
Biden called the students she met at the school "inspiring" and "so well behaved. I couldn't get over it. Early childhood education is so important to lay the foundation for all of our students."
They both reviewed drawings made by the children of famous landmarks, including the White House. Biden pointed out where her bedroom was at the White House.
Along with the roundtable, the two women visited about 30 4- and 5-year-olds at the school and saw how the children cared for bunny rabbits.
Teacher Dave Masters and four of the students tended to the rabbits while in their pen with Biden and the duchess. The women both commented about the large size of one bunny, named Storm.
Biden gave students a bowl of carrots to feed the hefty Storm while the duchess asked about the care of the bunnies. The outdoor area of the school had several separate rabbit pens, where the students took care of them as part of their daily routine, Masters said.
The president and first lady are expected to meet Queen Elizabeth II on Sunday. Biden turned back a question about meeting the queen.
When asked if she asked the duchess for advice on meeting the queen, Biden said: "No I didn't. We've been busy. Were you not in that room? We were talking education."
Students presented both women with flowers as they left the school and departed separately.
Biden has talked in the past about the struggles students face when they don't have a solid foundation in early childhood care and education. She said she and the president are committed to making sure all children gain those early skills that will improve their future.
Kensington Palace said Kate Middleton has been examining first-hand the root cause of many of today's hardest social challenges for the past decade, including poor mental health, addiction, the breakdown of the family and homelessness, and how those can be traced back to the early years of life.
The duchess is expected to make a major announcement highlighting the importance of early childhood, the palace said.
British experts who participated in the roundtable include Eamon McCrory, of the University College London; Trudi Seneviratne, of the Royal College of Psychiatrists; Ed Vainker, of the Reach Foundation; and Owen Thomas, of the organization Future Men.
U.S. experts joining on Zoom included Miriam Calderon, of the Department of Education; Miranda Lynch Smith, of the Department of Health and Human Services; Katie Hamm, of the Administration for Children and Families.