Pre-speech and back-and-forth: how babies learn to converse

Before a baby says their first word, they have typically been practising conversation for months. Not with words, but with the structure of conversation: one person vocalises, the other responds, then the first goes again. This back-and-forth interaction — sometimes called serve and return — is the scaffolding on which language is built, and it starts from the first weeks of life.

What serve-and-return means in practice

The term "serve and return" describes the interactive pattern where a baby does something — makes a sound, reaches toward an object, looks at you, changes expression — and a caregiver responds in a way that matches or builds on it.¹

A three-month-old coos. You coo back, or raise your eyebrows, or say "oh really?" in an animated voice. The baby coos again. You respond again. That is a conversation. The content is nothing. The structure is everything.

This pattern of responsive interaction builds neural connections in the developing brain — specifically the connections involved in language, communication, and social processing.¹ The more consistently a caregiver responds to these early bids for interaction, the more practice a baby gets in the foundational rules of communication: timing, turn-taking, reciprocity.

Parentese: why the silly voice is actually useful

The exaggerated, melodic, higher-pitched speech most adults instinctively use with babies has a name: infant-directed speech, or parentese. It features slower tempo, wider pitch range, elongated vowels, and simpler sentence structure than normal speech.

It turns out to be well-calibrated to exactly what babies can process. The exaggerated pitch contours capture and hold a baby's attention in a way that flat adult speech does not.² The simplified vocabulary and slower tempo give the baby a cleaner signal to parse. The fact that adults default to it across cultures suggests it is a genuine adaptation, not a stylistic quirk.

Talking to your baby in parentese is not silly. It is appropriate. Babies in environments with more responsive, animated speech develop language somewhat earlier than those with less — not because their parents were more intelligent, but because they had more practice extracting the patterns.²

Eye contact and the role of attention

Joint attention — when a baby and caregiver both focus on the same thing at the same time — typically emerges around 9–12 months and is one of the strongest early predictors of language development.³

Before joint attention appears, something simpler is happening: face-to-face eye contact during interaction. Babies prioritise human faces from birth, and the back-and-forth of eye contact during caregiving interactions is an early form of social coordination that sets the stage for joint attention later.

When you interact with your baby face-to-face — during feeding, nappy changes, play — you are doing something developmentally important even when it looks like nothing much is happening.

The milestones of pre-speech

The trajectory from newborn vocalisations to first words follows a recognisable sequence:³

• 0–2 months: Crying and vegetative sounds; startles to sound
• 2–3 months: Social cooing — vowel-like sounds in response to interaction
• 4–6 months: Babbling begins with single syllables; laughing
• 6–9 months: Canonical babbling — reduplicated syllables ("bababa", "mamama")
• 9–12 months: Variegated babbling with changing consonants; gesture and vocalization together; responding to their name
• 12 months: First meaningful words, typically "mama", "dada", or a consistent word for something familiar

The shift from babbling to first words is not sudden. Many babies produce "proto-words" — consistent sounds that mean something specific to them before they are standard words — before their first recognisable word appears.

When to mention it to your doctor

Speak to your GP or health visitor if your baby:

• Is not babbling by 9 months
• Is not using any words by 15–18 months
• Is not pointing, waving, or using gesture by 12 months
• Has lost language or babbling they previously had

Earlier assessment is better. Speech and language therapy, if needed, is most effective when started early.

← Back to the overview: Child development overview

Also in this cluster: Language development 0–12 months · Social smiles and attachment

Sources

1. Centers for Disease Control and Prevention. "Developmental Milestones." CDC, 2024. https://www.cdc.gov/ncbddd/actearly/milestones/index.html
2. NHS. "Speech, language and communication: baby's development." NHS, 2024. https://www.nhs.uk/conditions/baby/babys-development/speech-language-communication/
3. American Academy of Pediatrics. "Language Development: What to Expect." HealthyChildren.org, 2024. https://www.healthychildren.org/English/ages-stages/baby/Pages/Language-Development-Whats-Normal-Whats-Not.aspx