Innocent childhoods are being "smashed to pieces" by the civil war in Syria, Samantha Cameron said after visiting refugees fleeing the conflict.
The Prime Minister's wife said she was horrified by stories she heard from those caught up in the violence during her visit to Lebanon as an ambassador for Save the Children.
She welcomed the work of a clinic for new mothers and pregnant refugees run by the aid agency in the Bekaa Valley and a specialist centre helping children deal with emotional trauma.
"As a mother, it is horrifying to hear the harrowing stories from the children I met today. No child should ever experience what they have," she said.
"With every day that passes, more children and parents are being killed, more innocent childhoods are being smashed to pieces."
Among the youngsters she spoke to were a 10-year-old girl who described seeing her mother die in the rubble of their shelled home and a 13-year-old who dragged her uncle's body from the street after he was shot.
Mrs Cameron - who has three children - also heard from a mother whose three-year-old son was shot by a sniper next to his six siblings as they fled Syria in a car.
Save the Children chief executive Justin Forsyth, who accompanied her on the visit, said: "Samantha Cameron's support as a Save the Children ambassador helps draw attention to the plight of children caught up in this terrifying conflict.
"Without more help, and quickly, we risk losing a generation of Syria's children."