I remember reading a story where Dean and Sam were born as werewolves (Mary was one and didn't know or hadn't told John, I think). John and Mary discover their sons' problem when Sam shifts in the crib and Dean shifts to show him everything's okay. John has to train his sons how to be hunters and not let other hunters find out who they are.

I honestly don't even remember if it's a Dean/Sam or a gen story, sorry.

I have search the creature:werewolf tag here and on sd-recs and haven't found it.

ETA - Found in comments! Thank you!