Children acquire language in a remarkably consistent sequence across all known languages: cooing → babbling → one-word stage (holophrases) → two-word stage → telegraphic speech → full grammar.

The sequence is consistent even in children with very different linguistic input, which suggests the trajectory is partly maturationally determined, not purely learned.

The critical period hypothesis: language acquisition is easiest before puberty, harder after. Evidence: late L1 acquirers (isolated children) never achieve full grammar. Late L2 acquirers have persistent accent and grammatical gaps. The biological window is real.

Related: [[linguistic-relativity-weak]], [[@quinn/zone-of-proximal-development]]