conscious thought doesn't have to be verbal, and in fact I'd expect "inner monologue" type people to be sapir-whorfed in a much stronger way than nonverbal thinkers
the part where I didn't follow was the presupposition that the baby brain thinks in any language at all; sure (assuming a computable brain) you can formalize it as a turing machine of some sort programmed in some sort of language, but it's not clear whether it's interpretable
(interpretable as in "interpretability problem")
and even then, you'd need to distinguish between the formal description and what the program/process experiences, for example suppose you're doing image recognition, that program won't be experiencing its own code
Sure if you're conscious, you'll experience a dumbed-down version of the whole machinery, but why would that experience necessarily be words instead of, say, some form of proprioception? Suppose you grab an apple, do your limbs beam words at you instead of a feeling of weight?