There have been many attempts to model and emulate human syntactic acquisition and processing, but the general consensus is that it cannot be done without presupposing some mechanism that enables hierarchical structure. The number of tokens a child needs to learn syntax is the tiniest fraction of the amount of tokens an LLM is trained on.

Humans can also lose parts of their language processing capabilities, without losing others (start at e.g. https://en.wikipedia.org/wiki/Language_disorder), which is highly suggestive of modular language development. The only question on which there isn't much consensus concerns the origin of that modularity. And humans can lose knowledge while still being able to speak and understand, or lose language while retaining knowledge.

LLMs don't have that at all: they predict the next token.