Help with getting stains out of prefolds?

•K• • Mom to a one son, one 🌈 daughter, and 3 LOVED angel babes. One of the nice girls. Fitness fanatic. All glory and praise to Jesus!🙏🏼🙌🏼❤️

I just recently bought the green mountain diapers brown edge prefolds.

With all of the other prefold diapers, I was able to put the still wet diapers on the clothesline to sun out any stains.

So with my brown edge prefolds (for some reason)- the stains are not coming out in the sun. Super weird, as we live in Southern California and there is no shortage of sun (or heat!).

Any words of wisdom on getting the stains out?