Blog preview card using clamped font

Hi, would like to get your opinion on font-sizes.

1. I prefer using rem for font-size so it scales nice with users setting in the browser. Is it a good practice to scale fonts according to vw size and clamp it to rem?
2. How can I easily apply a base text size? Will the code below scale every child font-size?

body {
font-size: 0.8rem;
}

@media (min-width: 40rem) {
body {
font-size: 1rem;
}
}

.child {
font-size: 1rem;
}

Thanks! Aleš