If you don't want to just list them for $20 or so on FB marketplace/Craigslist, you can donate them! Some organizations around here (like the Florida Springs Institute) accept donated masks & snorkels etc to distribute to folks who may not otherwise have access. I think some other folks mentioned Diveheart - you can also ask around your local area for organiziations (Boy/Girl Scouts, local schools, YMCA, etc) that would appreciate them. Most teens are wearing adult sizes, so the shoe size shouldn't be an issue.
Some of our local dive sites also have a "donation/free pile" (i.e., for lost-and-found belongings that were never claimed) - I've seen snorkels and masks etc appear there, could consider adding your fins.
Some of our local dive sites also have a "donation/free pile" (i.e., for lost-and-found belongings that were never claimed) - I've seen snorkels and masks etc appear there, could consider adding your fins.