The Cambridge children, including a sometimes cheeky Prince Louis, were all on best behaviour as they were welcomed to the new school they'll all attend together.
But ahead of the big day a small press pack of one TV camera, one photographer and one reporter, were invited into the grounds, as the Duke and Duchess of Cambridge took their three children for a settling-in session.
The five of them were filmed walking along a path in front of the school to meet the headteacher, Jonathan Perry.
Four-year-old Louis, who's beginning full-time education and his nine-year-old brother and seven-year-old sister, all looked confident and happy, and even mum and dad were smiling too as they all seemed to chat away.
William called his children "all the gang" as he ushered them up the steps of the large white 19th century country mansion, and said the three of them were looking forward to starting.
"Welcome to Lambrook," Mr Perry told the children. "It's lovely to have you with us. We're very excited for the year ahead."
Shaking them each by the hand in turn, he asked: "Are you excited?" with all three replying "Yes."
William remarked: "We're looking forward to it," adding the children had "lots of questions".
The open afternoon was a chance for the children to meet some of the other new pupils, and also no doubt an opportunity for new parents to get used to the fact they may see Prince William and Kate at the school gates.
Prep school Lambrook, set in 52 acres of grounds, prides itself on giving pupils the "feathers to fly", helping their students aged from three to 13 to become confident, intelligent and creative young people.
Melanie Sanderson, managing editor of the Good Schools Guide, says it will tick a lot of boxes for William and Kate, who decided to move to Windsor in order for the children to have more privacy.
She told Sky News: "The Cambridges' first priority at this point in the children's development is that they retain that normality, so I think they can expect to be selected for matches the same as their peers.
"Mum and dad will be on the sidelines cheering them on, the same with school performances, concerts and plays, but on top of that, the school will prepare them for a life of public duty, and it has a very socially conscious feel to it.
"Jonathan Perry is incredibly focused on ensuring his pupils understand their situation, that they all understand their privilege, and you know, let's be under no illusion, we're talking about an incredibly privileged cohort here.
"The Cambridges may find themselves in a situation where they're not the wealthiest family in the school and probably won't have the biggest house either - so he has his work cut out educating the children that they are privileged and that they have a duty to use that appropriately."
Princess Charlotte was also seen on various occasions seeming to tell off both her brothers.