WriteGirl was the first resource I found as a writer, and becoming a member really pushed me to explore what creative writing was.
This organization is based in LA, but with COVID, all of their monthly workshops have moved online and as a result, they've welcomed girls from other areas as well! The workshops are always overflowing with support and good energy, and all in all it's awesome to gather with other young writers and interact with their famous guests. They also have an optional program where they can match you with a writing mentor, and I have had the best times with my mentor, Nina, in our weekly sessions. In addition, they have a form to submit your work so that whenever organizations come looking for writing, yours will be considered. And for juniors and seniors, they offer leadership opportunities and college help as well!
Unfortunately there isn't a program for boys quite yet, but from the looks of their website it's in the works! However, there are the WriteGirl Planets Magazines that are free for anyone to read under their Clubhouse page. For girls who would like to become a WriteGirl or would like more information, here is their website. It's really amazing to me that membership is free consider all you get out of WriteGirl, so I would highly recommend you guys take advantage of this opportunity/resource. :)