What exactly is going on with these twins? Would this be an example of Idioglossia?

I’m no expert by far but I would be tempted to say no this isn’t an example of idioglossia…purely based on the idea that the ‘language’ doesn’t have any meaning. Now one could argue that it does mean something to the babies, but I doubt it. It looks like they are simply exploring sounds, inflections and bodily movements. Other babies do this too but I wouldn’t say it’s a specific language…

They’re imitating grown up speech patterns and inflections, but they are repetitive in the sound they are making. They are really making fun of their parents, most likely their mother.

Probably not. They look a bit young to have nailed language in general.
Three clicks later, and I was in the weird part of youtube. XD

I don’t think so. The twins were imitating posture and sound and intonation, but other than that, they only had one syllable they were using: “bah.” I don’t think they were making fun of anyone, either. They were trying stuff out. They were playing.

I think it is kind of impressive that they were playing in this way at such a young age. I’ve played games like that with my kids, both when they were toddlers and, I think, when older, although not so much lately.

I think this might provide evidence that some linguistic principles are built into us genetically. Things like sentence pattern and the rising tone to indicate a question. But then again, I’d want to see a lot more evidence before I was sure about that.

@wundayatta I’d say tonality and inflection are strictly learned. They have heard it since in utero.

I don’t think so. I just think the one started making weird noises so the other laughed and tried to repeat it. Just like when an adult is trying to make a baby laugh. It always tries to repeat it, because it thinks it’s funny.