For those of you considering this name, some interesting things I thought you should know.
this name lists the name as an Irish Feminine name meaning Girl. however, In Scottish-Gaelic it was a masculine name, and some say it is an etymilogical pre-cursor to Colin. not sure on that. however, I do know that it was used as a man's name on at least one treaty in 1560.
Also, I've seen it used for men in modern day Hungary. Don't ask me how or why on that one. In anycase, there's a sight difference in how the two names are pronounced. The Irish, Cailin is a long a sound, and the Scottish, is more of an (Ah) sound. Interesting stuff, considering the groups came more or less out of the same cultural roots.
Cheers!
oni