Kate and William are moving to the Grade II-listed four-bedroom house on Windsor’s private Home Park.
They hope it will allow their children – Prince George, Princess Charlotte and Prince Louis – more freedom when they start at Lambrook School near Ascot, Berkshire, next month.
The Cambridges will retain their 20-room Kensington Palace apartment as their official working residence.
They will also have their 10-bedroom Anmer Hall country mansion near Sandringham.
Republic, a pressure group campaigning for electing a head of state, condemned the move.
Prince William and Kate have come under fire
PA
Prince George, Princess Charlotte, Prince Louis, Prince William and Kate, Duchess of Cambridge
Victoria Jones
Chief executive Graham Smith said: “While ordinary households are struggling with their energy bills and facing crippling inflation, why are we giving yet another home to William and Kate?
“This is disgraceful.”
He added: “All these palatial homes require round-the-clock protection, heating and staffing.”
He said the Crown Estate was “a state-owned property empire that is supposed to make money for the Treasury”.
The Queen has given her permission for Kate and William to lease the property from the Crown Estate.
It means the couple will pay market value rent using their own private funds.
Joe Little, managing editor of Majesty magazine, said the move has many benefits for the family including privacy and security.
Mr Little said: “Relocating to Adelaide Cottage in the ultra-private Home Park at Windsor takes away the ‘goldfish-bowl’ aspect of the Cambridge family’s life.
“Apartment 1A at Kensington Palace is perfect in so many ways but the Duke and Duchess and their children are unable to come and go as they might like or take advantage of the nearby London parks because of the ever-present privacy issues.”
He added that having all three children at the same school made sense and would remove the “nightmare” journey from Kensington Palace to Battersea twice a day.
“It also means that the cost of security, always a contentious topic, is much lower than if Louis was at a different school to his siblings,” Mr Little said.
The Crown Estate, which owns property worth around £14.4billion, is land and property owned by the sovereign but not in the private possession of the Queen.
It is not managed by the Queen, but its income does have some bearing on how much money she is given each year.
Under the Sovereign Grant funding formula, which pays for costs such as royal household salaries, official travel and the upkeep of royal palaces, the Queen receives a percentage of the Crown Estate profits for her official expenditure.
To help pay for a £369million refurbishment of Buckingham Palace, the percentage of the Crown Estate profits paid to the Sovereign Grant was increased from 15 percent to 25 percent for 10 years starting in 2017.
The rest of the profits go to the Treasury.