They flew in a private chartered plane with William and Kate and landed at a rainy Warsaw Chopin Airport.
The children could be seen peering out of the plane when it landed.
Charlotte was carried by her mother down the plane’s steps as George held his father’s hand.
The little prince and princess were smartly attired with the future king wearing a shirt and shorts while his sister wore a summer dress.
Waiting at the bottom of the steps to greet them was Britain’s ambassador to Poland Jonathan Knott and his wife Angela, as well as the diplomat’s Polish counterpart in Britain Arkady Rzegocki.
Two-year-old Charlotte and three-year-old George have not been seen in public since their appearance on the balcony at Buckingham Palace to watch the Trooping the Colour ceremony last month.
The trip will also take them to Germany and is another milestone in their lives because it is the first time they have been on an official tour of Europe.
It is not the first time William and Kate have taken their children on tour – they travelled to Canada in 2016.
The young prince also flew with his parents to New Zealand in 2014 in their extensive visit.
During the Poland and Germany tour the youngsters will only be seen during arrivals and departures.
This will be the last time the royal couple will be able to take their children on tour.
George starts school in South London in September and will attend Thomas’s School in Battersea and it is likely his sister will be enrolled in a nursery.
William and Kate’s trip, taken at the request of the Foreign and Commonwealth Office, is likely to be seen as another Brexit diplomacy tour in a bid to maintain and strengthen the UK’s relations with Europe as the UK departs from the EU.