Most advice about raising a bilingual child focuses on talking. Speak the language at home. Read aloud at bedtime. Look for playgroups, relatives, trips back to the country where the language is spoken. All of that is real and it matters. But it also leaves out something that turns out to carry more weight than it first appears to: whether a child ever learns to read and write in that language, not just speak it.
If your child speaks your heritage language but has never learned to read or write it, this is worth sitting with, because the research on what happens next is more specific, and more useful, than most parents realise.
Spoken fluency and literacy are not the same skill
A child who can hold a conversation in a language is not automatically on a path to reading and writing it. These are separate skills, built through separate kinds of practice, and a child can be genuinely fluent in speech while remaining entirely unable to read a single word.
This matters because most heritage language exposure, quite naturally, happens through speech. Parents talk to their children. Grandparents tell stories. Conversations happen at the dinner table. Almost none of that builds literacy, because literacy requires its own dedicated exposure: seeing the language written down, sounding out letters or characters, and eventually reading independently.
For many families, this gap goes unnoticed for years, simply because a child who speaks the language well seems, on the surface, to be doing fine.
Literacy gives a language a second, more durable foundation
Researchers who study heritage language maintenance across generations have found that literacy plays a distinct and significant role in whether a language survives into adulthood, separate from how fluently a child speaks it as a young child.
Part of the explanation is practical. A child who can read in the heritage language can engage with it independently. They can pick up a book, read a message from a relative, or follow along with a story without a parent mediating every interaction. Spoken language nearly always depends on someone else being present to speak it with. Written language does not. A book stays on the shelf whether or not anyone is available to read aloud that day, and a literate child can simply pick it up.
There is also a less obvious effect. A language a child can read starts to feel different to them, not just a way to talk to family, but a real language with its own place in the world, the same status that the school language has always had by default. Spoken-only languages tend to stay confined to the home. Written languages travel further, into books, letters, and eventually a child's own independent reading choices.
Speech alone is more vulnerable to erosion over time
One of the more sobering findings in this area is how differently spoken and written fluency tend to hold up over time.
Spoken fluency in a heritage language, when it is not reinforced by literacy, often narrows gradually across childhood and adolescence. Vocabulary shrinks to the range that gets used at home. Certain topics, especially anything more abstract or academic, become difficult to discuss because the child never encountered that vocabulary anywhere outside conversation. By adulthood, many heritage speakers describe feeling fluent for family conversation but stuck or embarrassed the moment a topic moves beyond it.
Literacy appears to slow this narrowing considerably. A child who reads in the heritage language keeps encountering new vocabulary, more complex sentence structures, and ideas beyond daily conversation, in the same way a monolingual child's vocabulary keeps expanding through reading long after their spoken vocabulary would have plateaued on its own. Reading does for a heritage language what it does for any language: it keeps feeding it material that ordinary conversation rarely supplies.
Writing does something conversation cannot
If reading extends vocabulary, writing does something slightly different. It forces a level of precision that speech rarely demands.
In conversation, a child can gesture, switch languages mid-sentence, or lean on context to get a point across, and often does, without ever noticing the gap. Writing does not allow for that. A child has to choose the exact word, spell it correctly, and build a complete sentence with nothing to lean on but the language itself. This is uncomfortable at first, which is often exactly why families skip it. But that discomfort is doing real work. It pushes a child to consolidate vocabulary and grammar they might otherwise have gotten away with only half knowing.
Families who eventually reflect on this often notice the same thing: children who write in the heritage language, even just occasionally, tend to speak it with more precision and confidence than children who only ever spoke it.
Literacy changes how a child feels about the language itself
There is an identity dimension to this that is easy to miss if you only think about literacy as a practical skill.
A child who cannot read or write a language they speak fluently sometimes comes to feel that the language is somehow less real, or less legitimate, than the one they read and write at school. This is not something children articulate outright. It shows up instead as embarrassment, reluctance, or a quiet sense that the heritage language belongs to a smaller, more private part of life than the school language does.
Literacy pushes back against that. A child who can read a story or write a birthday card in their heritage language experiences it doing everything a language is supposed to do, not just being spoken at home, but existing on a page, holding stories, carrying meaning independently of any one conversation. That shift, from a language that only exists in the room with you to a language that exists on its own, tends to change how seriously a child takes it, long before they are old enough to explain why.
Starting small still counts
None of this requires a formal curriculum or years of structured lessons. Families who maintain heritage language literacy tend to do it in the same low pressure, embedded way they maintain everything else about the language: books kept around the house, letters written to relatives, a bedtime story that is sometimes read rather than only told.
What seems to matter most is not intensity but consistency. A child who occasionally sees the heritage language written down, sounds out a few words here and there, and slowly builds toward independent reading over years, tends to end up in a very different place than a child for whom the language only ever existed as sound.
It rarely feels urgent in the moment. A three year old who cannot yet read in any language is not behind on anything. But somewhere between early childhood and adolescence, there is a window where literacy either takes root or does not, and unlike vocabulary, once that window closes, it becomes considerably harder to open again.
This article is for general educational purposes and does not replace advice from a qualified professional. If you have concerns about your child's development, speak with a paediatrician or a speech and language therapist experienced in bilingual children.
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