Welcome to BYC. Glad you decided to join our flock. You're Cuckoo Marans are too young to sex at this point. I would suggest posting their pics again on our What Breed or Gender is This? section at https://www.backyardchickens.com/f/15/what-breed-or-gender-is-this after their barred feathers come in. Typically females will have dark barring, males will have light barring. Please feel free to ask any questions you may have. We are here to help in any way we can. Good luck in getting pullets.