syntax 101 for babies

ken writes: The other day I was fooling around with Hugh and pondering the question why babies like to be jiggled. My theory comes from noticing something about Dot. When she was heavily pregnant, if she laughed her whole belly shook like a DIY store paint mixer. Hugh must have thought we lived on the San Andreas fault. But at the same time, Dot’s laughter must have flushed happy hormones through his system as well as hers, so he’ll have a positive association with being shoogled as a result. Maybe that’s way off the mark, but it has a comic appeal. Anyway, what interests me now is how I was pondering this with Hugh in my arms. He does like to be jiggled, so I jiggled him as I asked the question aloud
Why… [jiggle]
…do… [jiggle]
… … babies like to be jiggled? [jiggle jiggle jiggle]
and I jiggled him vigorously (I did NOT shake him) as I said the last part of the question more quickly than the two initial words.
This was quite unselfconscious while I was doing it, but after I had done it a few times, I realised how I’d broken the sentence into question word, auxiliary and propositional complement. These boundaries come naturally if you know the language. For him the pauses in speech and the additional stressing by jiggling probably show only that the sentence has parts, and perhaps the order in which important parts come in English (head first?).