Voice-first AI interaction is often presented as a natural and efficient way for humans to communicate with artificial intelligence systems. This contribution does not reject voice interfaces or speech-to-text technologies. Voice may provide access, immediacy, and participation, especially for users who cannot comfortably type, write, see, or sustain manual input. However, in Human-AI Cognitive Development, input mode cannot be treated as neutral. This contribution introduces a structure-first distinction between voice as accessibility support and voice as convenience-first cognitive bypass. It proposes that when expression becomes too easy, thought may enter action before it has been structured, tested, separated, or made visible. Typing and writing can function as cognitive stabilizers because they slow the transition from thought into language and allow reasoning to remain visible long enough to be checked and continued. Voice-first interaction, by contrast, may create mixed processing in which thought moves rapidly through speech, transcription, AI interpretation, and action before the human has fully formed the meaning. The contribution argues that the future of Human-AI interaction should not only ask how quickly intention can be expressed. It should also ask whether thought remains structurally intact while being expressed.