No. But if you're asking, something probably prompted the question — a comment from a family member, a moment that caught you off guard, a nursery worker who raised an eyebrow. The concern usually comes from outside as much as inside.
Here's what's actually going on.
What code-switching is and why toddlers do it
Code-switching is when a speaker moves between languages within the same conversation or sentence. In toddlers it often sounds like "more lait" or "je veux the ball" — words from one language slotted into the grammar of another, or a full switch mid-thought depending on who they're talking to.
To an adult, this can look like confusion. It isn't.
A toddler who mixes languages is doing something quite sophisticated: they are drawing on every linguistic resource available to them in order to communicate. If the word comes faster in one language, they use it. If a phrase feels more natural in the other, they reach for that. They are solving a communication problem in real time, with the tools they have.
That's not a failure to separate the languages. It's evidence that both languages are present and accessible, which is exactly what you want at this stage.
What the research actually shows
Studies in bilingual language development are consistent on this point: code-switching is a normal phase, not a warning sign. It reflects how the developing brain organises and accesses multiple language systems, not a failure to keep them apart.
One of the most reassuring findings in this area is that bilingual children are capable of separating their languages. They demonstrate this regularly: speaking one language to one parent, switching to another for a grandparent, adjusting instinctively based on who they're with and what the context demands. The mixing that happens isn't because they can't tell the difference. It's because in many moments, they're choosing not to. Because mixing gets the job done.
Code-switching also tends to decrease naturally over time, as vocabulary grows in both languages and children become more aware of which language belongs in which context. You don't need to eliminate it. It resolves on its own with consistent exposure.
Where the concern usually comes from
The anxiety around code-switching is often less about what's happening with the child and more about what's being said by people around the family.
Grandparents who were raised monolingually may read it as confusion. Nursery workers unfamiliar with bilingual development may flag it as a concern. Other parents may offer opinions based on what they've heard rather than what the research shows. And because the mixing is visible and audible in a way that the underlying development isn't, it's easy to fixate on as a problem.
It helps to know that the researchers who have spent careers studying how children acquire multiple languages are not worried about code-switching. The parents in the bilingual parenting community who have been through this phase are not worried about it either. It is a normal, temporary feature of a process that is working.
What not to do
Correcting code-switching directly tends to be counterproductive. A child who is mid-sentence, reaching for a word, using what they have to say what they mean, stopping that flow to ask them to say it differently introduces pressure into a moment that should feel effortless.
Children who are frequently corrected on language mixing often become more hesitant to speak, not less likely to mix. The confidence to use a language, and eventually to use it correctly, grows in low-pressure environments. It shrinks under scrutiny.
If your child says "more lait" and you want to gently model the full phrase, the most effective way is simply to respond naturally in the language you're using: "you want more milk? here you go" or "tu veux plus de lait?", and continue the conversation. The correct form is offered without the interaction being interrupted. Over time, that modelling is what shapes the output.
What about random sounds and filler words?
Some parents notice something slightly different from classic code-switching: their child fills gaps in sentences with sounds that aren't quite words in any language. Not mixing real words from two languages, but using what sounds like plausible nonsense to hold a sentence together.
This is a recognised behaviour and it's not a cause for concern. It even has a name — researchers sometimes call them placeholder or filler sounds — and it's more sophisticated than it looks.
What's likely happening is that your child has already acquired the rhythm and structure of a sentence before they've acquired all the words. They know roughly how long the sentence should be, where the stress falls, what the overall sound pattern is, and they fill the gaps with sounds that fit that template. Real words where they have them, phonetically plausible placeholders where they don't. It's a scaffold, not a gap.
The more interesting thing — and something bilingual parents sometimes notice before researchers named it — is that the filler sounds are often not random at all. They tend to belong to the phonetic inventory of one specific language. Sounds that exist in Korean but not in French, or vice versa. If you listen closely and the nonsense sounds feel like they belong somewhere, they probably do. The brain is holding a slot open in the right language while the actual word is still being acquired.
You and your partner may not even agree on which language the sounds belong to. That's common, and it makes sense: a child with exposure to multiple sound systems will produce fillers that sit in a phonetic space influenced by all of them.
The only time filler sounds are worth paying closer attention to is if real words aren't developing alongside them over time, or if the jargon is increasing rather than gradually being replaced by vocabulary. In typical bilingual development, the placeholders fade as the words arrive.
What actually helps
The single most effective thing you can do is keep both languages present, consistent, and connected to things your child genuinely enjoys.
Vocabulary gaps are one of the main drivers of code-switching. Children mix languages partly because they don't yet have the word they need in one of them. Building vocabulary in the minority language, through routines, songs, stories, and play, gradually reduces those gaps. The mixing doesn't stop overnight, but it does reduce as the language becomes richer and more retrievable.
Repetition is particularly important here. A word a child has heard once is a word they might reach for in the moment of need. A word they've heard dozens of times, across different contexts, in a voice that feels familiar — that word is theirs. It's available without effort. The more words that feel that way in the minority language, the less the child needs to borrow from the other one.
Play remains the most underused tool in this. A child who mixes languages under the mild social pressure of direct conversation will often use the minority language more naturally and more fully during songs, games, and independent play, when no one is watching and the goal is fun rather than communication. Those moments of unselfconscious use are where language settles in most deeply.
The bottom line
Mixing languages is not a problem to fix. It is a normal, temporary feature of bilingual development that resolves on its own as vocabulary grows and exposure continues.
What your child is showing you when they code-switch is not confusion. It is fluency in progress: two languages present, accessible, and being used together while the separation is still being worked out.
Keep both languages warm and consistent in their life. The rest follows.
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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