Babies who are yet to master linguistic skills can still communicate with their parents to let them know if they are hungry or want to sleep.
"Przepraszam" (excuse me), "sprzatamy" (cleaning up) ou "kurczaczek" (chick), are practical words to know but impossible to pronounce for one-year-olds, even if they are Polish.
"Babies aren't ready to speak. In order to utter words you need teeth," Danuta Mikulska, 31, a linguist specializing in sign language told AFP. "Their muscles and vocal chords are insufficiently developed, but they are able to make hand gestures."
At nine months, Mateusz has already mastered a few signs: suck, balloon, music, light. "He understands twenty-or-so more," says his mum, Agnieszka Nec, 25.
When eight-month-old Adam wants something he spells it out with his hands. "It's with gestures that he tells me he wants a song or to be rocked when he's going to sleep," says mom, Karolina Olszewska, a journalist.
Along with eight other babies and their mums, none of whom have hearing problems, Mateusz and Adam learn sign language at Warsaw's Klub Koko, created by three women, academics and artists: Danuta Mikulska, Magdalena Jakubowska and Joanna Kolodziejska.
During a series of hour-long lessons, instructors create a world of play for babies and moms focused on songs, poems and exercises in which words are systematically reinforced by their equivalent hand signs.
According to Klub Koko, the method first created in the United States in the 1980s reinforces contacts between mother and child, stimulates the intellectual and sensory-motor development of babies as well as their imagination, memory and concentration.
It reduces tears, tantrums and frustration in tots, who, try as they might, cannot get their message across verbally, instructors say. It also helps toddlers master the ability to speak, read, write and count more rapidly.
When they have already learned that the sign "house" corresponds to an actual house, they've already done the conceptual work," Mikulska explains. "When they will be ready to speak, they won't need to do the work again in their head."
For sceptics who ask whether baby and toddler sign language might inhibit speech development as tots get used to signing, advocates give a resounding "no" and point to widely cited US research at the University of California. These studies showed that symbolic gesturing -- as it's called -- even facilities the early stages of language development.
Since 2005, Mikulska has been using sign-language to communicate with children without hearing impediments and is currently writing a doctorate on the topic at the University of Warsaw.
Mikulska is part of a group of experts lobbying for Poland to officially recognise sign language as a linguistic minority as it already has been elsewhere, notably Austria where it is even recognised in the constitution.
"Our activities also serve to promote sign language in Poland and to educate people about the reality of deaf and mute people," says Mikulska. "These children could be sign language interpreters in the future."
Agnieszka Nec has already caught the bug: "Mateusz has learned things, but I have as well and I intend to keep on learning sign language."
At eight months, little Adam certainly still has difficultly in signing gracefully.
"But when he invents his own gesture, I tell myself that it is already his own personal contribution to sign language," says Karolina Olszewska with a smile.