A Kensington Palace statement said they were accompanied by their parents to “settle in for the afternoon” at the prestigious Lambrook School near Windsor.
The annual event will be held to welcome new students and their families to school before the first day of term, the statement added.
Cambridge kids officially started school on Thursday.
Prince William and Duchess Kate entered school with their children on Wednesday before being greeted by principal Jonathan Perry.
“Welcome to Rambrooke,” Perry said to his children, reports the PA Media Agency. “It’s an honor to be with you. I’m really looking forward to next year.”
He waved each hand and asked, “Are you excited?”
“Yes,” they said, PA reports.
“We’re looking forward to it,” William said, adding that the kids “asked a lot of questions.”
George and Charlotte attended Thomas’s Battersea, a paid school in south London.
The decision to move the children’s school was announced by Kensington Palace in August.
They live in Adelaide Cottage, a four-bedroom house on the grounds of Windsor Castle in Berkshire, about 25 miles from London.
A royal source told CNN that the move will allow William and Katherine to be “active parents in a busy school.”
“They want to be as normal a family as possible,” the source added.