Okay kiddo, so let me explain monetary inflation like you're five years old!
Imagine you have a bunch of toys, and you want to buy more toys with the money you have. But suddenly, the prices of the toys go up -- this means you can't buy as many toys with the same amount of money anymore. This is kind of what's happening with monetary inflation!
Monetary inflation is when the amount of money in an economy increases a lot, which usually happens because the government prints more money or makes it easier for banks to create loans. When there's more money around, people have more money to spend, but businesses can also raise their prices because they know people will pay more.
So when there's a lot of monetary inflation, the prices of things go up and up, and the money you have can't buy as much anymore. It's like if the price of your toys suddenly doubled overnight, and you could only afford half as many toys as you could before!
That's why economists try to keep inflation low and steady, so that the prices of things stay stable and your money can still buy the same amount of stuff. Does that make sense, little one?