Okay kiddo, so a long time ago, in the year 1991, something really scary happened in a place called Downing Street. Downing Street is a very important place in the United Kingdom because it's where the Prime Minister of the UK lives and works.
Some bad people decided to do something very bad and scary by trying to hurt the Prime Minister and other people who were working in Downing Street. What they did was they secretly fired something called a "mortar" which is like a really big and dangerous firework, into Downing Street.
Luckily, no one was hurt because the people who were trying to protect Downing Street from bad people were able to stop the attackers and catch them. The police were able to catch the people who did this bad thing and put them in jail to keep them from hurting anyone else.
So, even though bad things can happen sometimes, good people are always working to keep us safe and stop the bad guys from doing harm to others.