Like others have said, this is something that falls under parental responsibility, together with cooking and cleaning. But just like with those things, there are many families who don't teach their children basic life skills. Or worse, the lives they lead are a bad example of those skills.
People put holidays on their credit card. People buy (non essential) clothes, TVs, sofas on their credit card. I'm not talking about those who then pay the bill in full the week after. I'm talking about those who decide to 'redecorate' because the furniture is a bit dated, and they have the credit to do so. A larger TV is what everybody else is buying, so let's buy one too. Top range phones on contract, new cars, the list goes on.
As a society, we have gotten used to get things the moment we want them. I want to find out something I don't know, I open my smartphone and have the answer within 10 seconds. Using google is free. Buying clothes, holidays, eating out, furniture and cars because I want them, isn't free. 'I want it, and I want it now' is how we as a society function nowadays. It's what we teach our children.
APR and mortgages and repayments should be taught in schools, yes. But more important than that is teaching our children that we don't buy things we can't afford. That means, we don't buy things we don't already have the cash for. Excluding big purchases and the protection that comes with using a credit card for those, credit cards are to be used in emergencies. A new sofa, carpet or TV is not an emergency. A boiler is, a food shop is, basic clothes are.
I wasn't taught at school about finances. I barely understand how interest function. I just know that I own a credit card (0% rate), and I don't buy anything on it unless there's an emergency. I have several thousands available to me in cards and loans. I'm reminded of them every time I open my banking app. But that doesn't mean I should spend them. The bottom line is, don't buy stuff you don't have the money for. THAT is what we should be teaching our children, and teaching starts with leading by example.