Seo é mo mhac. Seo í mo mháthair. Seo iad mo theaghlach. Seo í mo chlann.

Are these not correct?

According to the little dictionary I'm currently using, Redwolf's suggestion seems to be right that "clann" is feminine whether you're referring to boys, girls, or both.

Merry Ploughboy, I say to be helpful and not for any other reason that the best way to learn is to use a textbook. Whatever version of Irish is given in the textbook, you can work your way through. Random questions can't really teach you a whole language. And dictionaries are not textbooks either - and cannot be used as such.

Clann is a feminine word - as you rightly say, the word is feminine whoever it refers to. But that does not mean that plural pronouns cannot be used with it.

See http://www.irishpage.com/story/Madra/madra(9).htm - for a famous story from the Munster Gaeltacht that one a prize in the 1901 Oireachtas: gurb iad mo chlann iad.

Irish dialects are so disparate that I'm starting to learn not to be emphatic about what is and what is not good Irish. There always appears to be an exception. I don't know if any dialect says "seo í mo chlann". Lughaidh has said that in Ulster the í would drop out anyway: seo mo chlann. I am not too certain over the validity of *seo í for Munster Irish. AFAIK it is sid í. But in any case: sid iad mo chlann is what dovetails with that quote from Madra na nOcht gCos.

What they say in the Connemara - that remains the one major dialect we need to pin down. Do they say seo í mo chlann, seod í mo chlann, seo iad mo chlann or seod iad mo chlann - or, potentially, all four? Bríd's example was of muintir (seod iad mo mhuintir), and so did not specifically use clann.

Sid iad mo chlann - is right - but not necessarily what every dialect will have. Looking in the dictionary and seeing clann is feminine is not going to clear up this query.

Well, frankly, I'm doing a little more than asking "random questions" and "[l]ooking in the dictionary and seeing clann is feminine." I am using RS as my main "textbook." I supplement that with http://www.erinsweb.com/gaelic1.html and http://www.phouka.com/irish/ir_intro.html. I use http://www.irishdictionary.ie/home and FOCLÓIR GAEDHILGE AGUS BÉARLA, as well as other resources I've collected along my way (including this forum and the occasional "native speaker" to try and chat with).

I don't feel like my questions are random, as I am putting them in the context of the resources I use above; in this way I'm sort of trying to imitate a classroom. If this is not the appropriate place to do that, then fine, though I'm not sure what an internet forum is better designed to do that to try and "clear up querys."

Yes. One of the native speakers RS hooked me up with recommended http://www.potafocal.com/Home.aspx; I have it saved as a bookmark.