This seems weird, but indeed this has happened in my uncle's family. All the kid's names (7 of them I think) start with "M" and I don't know why! Anyway, have you seen this, or have you seen something similar like say, all the kids having the same middle name? OK, well this can become creepy!
All my brothers have names that start with the same letter. I would have followed but a different name came to my mom's mind. Our middle names all start with the same letter though.