2 Multilingualism and siblings
We might expect children growing up in multilingual households to have lower vocabulary levels compared to their monolingual peers, simply because there are only so many hours in the day, and an hour spent learning the words of one language is an hour spent not learning the words of another. However, there is some evidence that growing up in a multilingual environment can give children a word learning boost (De Houwer, 2021; Tan et al., 2024). The basic idea is that if children have already made the connection between the English form ‘bird’ and what it means, for instance, then it might be relatively easier for them to connect the German ‘Vogel’ to the same underlying concept, compared with learning this connection for the first time. Interestingly, learning a sign language does not also seem to delay the acquisition of spoken languages either for children simultaneously learning both. The kind of ‘mental juggling’ of their languages multilingual children engage in can present both challenges and opportunities (Byers-Heinlein et al., 2019).
Many parents wonder whether growing up with two or more languages might confuse their child. The research says otherwise.
Transcript: Video 1 Is learning multiple languages confusing my kid?
SPEAKER 1: No.
SPEAKER 2: No. [NON-ENGLISH SPEECH]
SPEAKER 1: [NON-ENGLISH SPEECH]
SPEAKER 2: Oh, wow!
SPEAKER 3: Hello, and welcome back, curious parents. Learning a language is such a big job. It’s a wonder that any of us learn just one of them. But what about two or even three languages?
SPEAKER 4: [NON-ENGLISH SPEECH] 1, 2, 3, 4, 5, 6, 7, 8, 9, 10.
SPEAKER 3: Many parents who use a mix of languages at home worry that this somehow messes with their little one’s language growth. Today in the Hello Lab, we explore a key question-- is learning multiple languages confusing your kid? Let’s get the scoop.
[MUSIC PLAYING]
You might be surprised to know that speaking more than one language is not uncommon at all.
[NON-ENGLISH SPEECH]
In fact, about half of the world’s population speaks at least two languages. But this is a bit of an educated guess.
SPEAKER 5: Where’s your mouth?
SPEAKER 6: Good job. [NON-ENGLISH SPEECH]
SPEAKER 3: Kids grow up in multi-language households all over the world, including in the US. But in the not-so-distant past, learning more than one language in early childhood had a, well, not so great reputation. Why? Early researchers thought that kids who were using two languages weren’t performing well on standardised tests of intelligence, compared to kids who just used one language. These kids seemed to struggle to speak, used language, and were-- cue those air quotes-- ‘behind’ cognitively.
But in 1962, a study reported just the opposite results, showing kids who were bilingual doing better than single-language kids. This new finding changed the game regarding the way we think about childhood multilingualism. Since then, many studies show that multilingualism might have some really cool perks for kids, including sharper attention, memory skills, and more flexible problem-solving abilities.
[NON-ENGLISH SPEECH]
One study even found that bilingual babies as young as six months did better than their monolingual peers on a memory task. But don’t get too excited just yet. It’s hard to say for sure what might account for differences between bilingual and monolingual kids. And bilinguals don’t always have a leg up across experiments.
For instance, one area that is still being explored is vocabulary. Keep in mind that there are many different kinds of vocab we can measure, such as what words a kid understands versus what they say out loud.
SPEAKER 7: Apple. Bear bear.
SPEAKER 8: [NON-ENGLISH SPEECH]
SPEAKER 9: [NON-ENGLISH SPEECH]
SPEAKER 8: What colour?
SPEAKER 9: Blue.
SPEAKER 3: Well, some research shows that bilingual kids might have a smaller vocabulary in a single language than their monolingual friends. But when looking at both of the languages they’re learning at the same time, the difference, more or less, evens out. And a very recent study suggests that even when comparing one language for bilinguals and monolinguals, the differences in vocab fade with time.
SPEAKER 10: Hamburger.
SPEAKER 11: Hamburger.
SPEAKER 12: Hamburger.
SPEAKER 11: Hamburger.
SPEAKER 3: There’s still a ton we need to learn about this before jumping to conclusions. Whether small differences in vocab exist or not, kids learning two languages tend to hit big language milestones, like saying their first words, at the same age as kids learning just one.
SPEAKER 13: Book.
SPEAKER 14: Book.
SPEAKER 13: Hedgehog.
SPEAKER 14: Hedgehog.
[NON-ENGLISH SPEECH]
SPEAKER 3: There’s also no evidence whatsoever that being bilingual directly causes communication- or language-based disorders. So if you’re currently raising a bilingual kid, you can breathe a nice sigh of relief. Despite everything we know, many people still think that learning two languages at the same time can somehow be harmful for overall language outcomes, though the data show that this myth may be fading in popularity.
SPEAKER 15: Tell mommy what you want. Are you hungry? You want more to eat? More to eat, OK.
SPEAKER 3: The science around this stuff is pretty clear. So-called language confusion is not a thing. What’s plain wrong here is the idea that learning another language delays language development or permanently confuses a kid. Now, this doesn’t mean that bilingual kids never mix up languages or confuse a word for another from time to time. If you’re a parent with a bilingual kiddo at home, you probably have plenty of funny stories of your little one doing just that. This isn’t a sign that something is wrong.
[NON-ENGLISH SPEECH]
In fact, kids are pretty great at distinguishing between languages. What might sometimes look like confusion, like switching between languages from sentence to sentence, is likely just a kid getting the most out of both.
SPEAKER 16: How about kiwi? That’s right. Fingerspelling about kiwi-- K-I-W-I. And she’s not really fingerspelling, but she’s trying.
SPEAKER 3: How? Compared to adults, young kids are absolute sponges when it comes to language. Trust us, there’s plenty of room in those adorable brains. Kids can learn tons of different words for the same thing without getting confused if they’re in different languages.
We don’t need scientific data to tell us that babies who are in single-language households learn different words for the same things too, like learning that their doggie is also called Captain Paws. Depending on a ton of different factors, a little bit of language mixing might sometimes make learning words a bit harder or easier for kids.
Learning a language is hard work, and it’s not just about what words you’re learning, but how you’re learning them that influences this process. Remember, the bottom line is that with time and strong language support from their parents, both monolingual and bilingual kids reach their language milestones at the same time.
Well, there you have it. Don’t let long-standing language myths fool you. If you’re speaking English, Spanish, Mandarin, Elvish, or Dothraki, your kid won’t be delayed or confused. They’re not just ready for this. Their brains are literally wired for it. And if you’re regularly mixing up languages at home with your little one, you might be giving their brain an extra boost in surprising ways. Until next time, [NON-ENGLISH SPEECH]
SPEAKER 17: Who likes her slippers?
SPEAKER 18: Me.
SPEAKER 3: Don’t just take our word for it. Check out our evidence library on our website to learn all about the research that helped us make this episode. Link in description.
Hey, not so fast. The question I asked at the start of the video still stands-- what languages do you speak with your little one in the home? Leave us a comment or tag us on social media to let us know. We love seeing what you guys come up with. Stay tuned for our next episode about language milestones and first words. And don’t forget to like and subscribe.
This video explored what the science tells us about childhood multilingualism – how children separate languages, build vocabulary, and reach milestones on time. Studies show that learning multiple languages can support attention, memory, and flexible thinking, without delaying speech or communication.
We might also expect children growing up with multiple older siblings to have slower vocabulary development, as parents have only so many hours in a day, and an hour spent talking to one child might be an hour not talking to another. However, if older siblings can already speak, then the language parents direct at their older siblings can trickle down to their younger siblings. There is some evidence that this can make up for any reduced direct parental language input. Thus, what seems more important than simple birth order is child-to-caregiver ratios. If older siblings can also act as caregivers to some extent, then rather than take away adult resources (time, care, attention) they can contribute positively to the household dynamics and language environment of the younger siblings (Rosslund et al., 2025).
These examples show that vocabulary development is full of dynamic complex relationships, where different causes can have different effects at different times development, a topic which is explored further in the next section.