"WE WILL MAKE SURE THAT THOSE WHO HARM US PAY A HEAVY PRICE": This was the message from the Israeli Ministry of Foreign Affairs. It was in an ad discovered by a 6-year-old boy playing a video game.

Maria Julia Cassis was sitting down to a meal in her terraced home in north London when her 6-year-old son ran into the dining room, his face pale.

The puzzle game on his Android phone had been interrupted by a video showing Hamas militants, terrified Israeli families and blurred graphic footage. Over a black screen, a message from the Israeli Ministry of Foreign Affairs told the first grader: “WE WILL MAKE SURE THAT THOSE WHO HARM US PAY A HEAVY PRICE.”