By Sally Blundell for Frank Film
We will walk. Without tuition or encouragement, we will take that first and precarious upright lurch into immediate space.
Talking, on the other hand, is a learned skill, requiring repeated conversation, intonation and a maximum distance of one metre.
"You've got to be close together," says sociolinguist Margaret Maclagan, adjunct professor at the University of Canterbury's New Zealand Institute of Language, Learning and Behaviour.
"The language has to be directed to the baby - they don't listen to something that's not directed specifically to them."
Maclagan has spent the last 40 years studying language development, "and still I find it completely fascinating", she told Frank Film.
At Shirley Playcentre in Christchurch, a noisy throng of under fives covered the gamut of language proficiency.
At eight months, Milo climbed the scale of intonation with a basic ah-ah-ah.
Initially, Maclagan explained, babies copied the intonation, the way speech went up and down, but the ah-ah-ah of a baby's first attempts at language were as much to do with physiology as they were with speech.
"A small baby's tongue is big compared with an adult's tongue. When a baby can sit up, the tongue flops forward and when the tongue is right forward you get an 'ah'."
Finn, aged nine months, made an impressive bah-bah-bah sound, often the first controlled sound a baby will make.
"Everybody thinks they are saying 'baby'," Maclagan said, "but actually all babies, all languages, make that sound."
The first word usually comes somewhere between nine months and 18 months. For Sydney, now 16 months, it was "dada", "even though I said mama all day," her mother, Annie, said. For Rachel's son Fletcher it was mum - "In my mind it was mum anyway."
Timing for that first word can vary. Having an older sibling can encourage language skills, while very active babies may be more focused on motor development than chattier loiterers.
But at any stage, parental interaction is key.
As Maclagan wrote in her book Talking Baby, co-authored with Anne Buckley, this exposure to language, and the "speech melody" of language, begins early: "Newborn babies would rather listen to the human voice than to other sounds, and as you talk to your baby they're learning to pay attention to you. And they're hearing lots of the language they're going to learn."
"If babies don't hear language, they won't speak," she said at the playcentre. "The brain is wired so we can learn language but we have got to have someone to copy."
Through repetition, validation, songs, rhymes, games, stories and just everyday simple conversation, a parent is laying out the roadmap of language, long before a baby will utter their first word. There is no need to copy cute pronunciations, Maclagan wrote in her book, or to correct faulty grammar. Rather it is about modelling and repeating day-to-day language through close one-to-one interactions.
"As you talk to your child, as you tell them stories, you're setting them up for life."
In families where English was not the first language, she said, it was important to speak to a child in the parent's first language.
"Your child will learn English later when they go to school or preschool but they will have a solid basis of language from your own language."
By 18 months, Maclagan said, most babies will have two words they can put together, but they want to say so much more.
"Children always understand more than they can say - especially at about 18 months they get really frustrated. Everybody's talking - and they want to talk too."
At 20 months, Fergus knew what he wanted to say, his mother Julia said, "but he can't actually say it. He can say 'no' really well, so he basically says 'no' to absolutely everything you ask him."
From here, more and more words are put together, sentences get longer. By the age of four, the actual structure of language is fully developed, even if the grammar - and logic - is a bit faulty.
"Babies can't talk," four-year-old Isaac at Shirley Playcentre said. "When I was a baby, I can't talk."