Ages matter. If the oldest can help out, it scales better.

But all pretense of democratic rule must be jettisoned once the kids outnumber the parents.

I agree, and watching larger families in my community (where my three kids is a "small" family), it's obvious that older siblings take a significant role in helping the younger. That said, the demeanor of kids matters a lot, as my oldest (teenager) is significantly more of a challenge than my other two. She by herself takes more energy than the other two combined.

Okay, you're our expert on this thread.

But note that the question is not if 3 kids are harder. They're obviously harder than 2.

The question is (for the sake of the analogy), if going from 2 to 3 is harder than going from 1 to 2 or 0 to 1.

We are talking strictly about incremental difficulty here.

Kids and languages aren't a reasonable comparison. None of us are born with children, but we are all born with language (of a sort, and yes I understand that opens the door to debate). On the topic of kids, going from 2 to 3 is significantly harder than going from 0-1 or 1-2, so much so that I'd say it was an unspoken factor in my divorce.

Without providing any hard research to back my thoughts, I'd also surmise that it is difficult to transfer this onto the difficulty of learning a language. My thinking on this is that if for example you are learning another language within the same family, that is a different level of difficulty than learning a language in a new-to-you language family. As a German speaker, there are other Germanic languages that look very familiar to me, where I could take a reasonable guess at the meaning. On the other hand if I were to learn Mandarin or Russian, it would be a significantly larger task.