The Duchess of Cambridge told schoolchildren she was finding her visit to the Somme "emotional," as she toured a new museum dedicated to those lost in the bloody battle.
Kate said the experience had been "very moving" as she met British and French teenagers attending the centenary commemorations at Thiepval, France.
She was touring a new visitor centre at the Lutyens-designed Thiepval Memorial to the Missing of the Somme with the Duke of Cambridge, Prince Harry and French President Francois Hollande.
The royal party met 24 of the 600 UK, Irish and French schoolchildren taking part in the commemorations and an Anglo-French educational programme organised by the British Council, which includes a week-long residential stay in the region.
Poppy Hodgson, from Hermitage Academy in Chester-le-Street, and Neave Heaton, from Greenfield School in Durham, presented William and Kate with a binder of art, photography and history work produced by pupils taking part.
Poppy said: "She said it was quite emotional being here and that they were really enjoying their visit. She said it was very moving."
Harry told students from St Paul's Community College in Waterford, Ireland, and Wolsingham School in County Durham: "It's important that you are here. There are all sorts of parts of history that are being forgotten.
"It's important for us to remember older history as well as more recent history. I'm actually quite jealous of you guys getting to spend five days here learning all about it.
"You will come back with a huge amount of knowledge."
The royals were shown around by the museum's vice-director Emilie Simon, taking in two dramatic 30 metre-long murals showing the preparation for and first day of the 141-day battle by the Maltese-American cartoonist Joe Sacco.
"Look at the detail," remarked Kate, taking in the intricate artwork.
They seemed fascinated by relics from the trenches displayed under a glass floor, including shell cases, sections of barbed wire, boots and horseshoes.
They were also shown a German machine gun, captured by British troops as a battle trophy on September 26 1916. Their guide explained that one of the soldiers who seized the enemy weapon was declared missing the following day and his name is among the 72,000 on the memorial to those whose remains were never found.
While Kate speaks good French, Prince Harry may need to brush up on his language skills, according to schoolchildren who met the royal visitors at Thiepval.
William, Kate and Harry met students marking graves in the cemetery at the Battle of the Somme memorial at the end of a poignant ceremony where the children laid wreaths and bouquets on each tomb.
After chatting to Kate, Kamelia el Alelga, 15, from Beauvais, near Paris, said: "Her French was very good. She asked my age, my name and if we all come from the same school."
She said the Duchess had also spoken about the service in English, adding: "She said it was really impressive and emotional. It was amazing to meet her - it was everything."
Berteel Py, 11, from Courcelles-les-Gisors, was also impressed by Kate's French, saying: "She asked me my name and my age and said she was happy to be here."
Berteel, who also spoke to Prince Harry, added: "He asked me if his French was good or bad. Of course I said it was good, but I didn't really understand what he was saying to me."