Play dates with the future king, however, are more complicated than the average, with every palace visitor having to be thoroughly vetted by security.
"It does involve a bit more planning than a normal play date, as everyone visiting the palace has to be security vetted," says the source.
Earlier this month, George's 4-year-old sister Charlotte joined her big brother at St Thomas's in Battersea in South London.
The Kensington Palace Instagram account posted the sweet first-day photos, and a video of her meeting one of her teachers to mark the momentous occasion.
St Thomas's in Battersea has 560 students aged from four to 13 and promotes the ethos "be kind".
Pupils can learn everything from art to ballet, drama, French and music with specialist teachers.
Headmaster Simon O'Malley said the school emphasised key values such as "kindness, courtesy, confidence, humility and learning to be givers, not takers".
"We hope that our pupils will leave this school with a strong sense of social responsibility, set on a path to become net contributors to society and to flourish as conscientious and caring citizens of the world," he said.
