I have seen single child households, but that was apparently a known bug posted on the AHQ, and not a mod issue. It has been fixed, because I haven't seen it in a good while. I was left with a lot of orphans, and moved them into a house with a single townie "caregiver". Probably not necessary, but didn't have the heart to just delete them. Figured I'd gather them all in one place, instead of them being moved into homes by themselves.
To be honest, I have tweaked MCCC a lot, because I didn't like what was happening. It was marrying off premades I had plans for myself, and 8 out of 10 couples were same gender. Now, I don't mind that, at least half my played sims are exactly that, probably more when I think about it. But it was too much. And it messed up my plans. The tweaking is probably why I don't have full families generated anymore, only single YA/A. I'll need to look into that.