Okay, kiddo, let me try to explain it as simple as possible! In September 2008, the world experienced something called a "global financial crisis." It all started because many big banks and financial institutions in the United States made risky investments in something called "subprime mortgages." These are loans that were given to people who may not have been able to pay them back.
Because of this, lots of people couldn't pay back their mortgages and had to leave their homes. This caused the housing market to crash, and banks lost a lot of money. This also affected other parts of the economy, like jobs and businesses.
People started to panic because they were worried they were going to lose their savings and homes. This panic caused the value of the stock market to drop rapidly. This led to a worldwide economic crisis, where businesses and people around the world were affected by the falling value of money and job losses.
Governments and central banks around the world had to put a lot of money into the banks to keep them from going bankrupt. The global financial crisis was a huge wake-up call for people to be more careful about how they invest their money and for governments to make sure banks are regulated properly so that this doesn't happen again.