Is earlier really better for language learning?
Much is made of the mythical sponge-like capacity of babies and children to learn multiple languages. Add this to the on-going quest to prove that bi/multilingualism is the cognitive brain boost that will have our children beating back Harvard and Cambridge, and you have a recipe for stress. I've met children who speak 2 languages at home, are going to school in a third, and are attending language classes to learn a fourth language in their spare time. Some are budding polyglots, some are stressed out and don't have a fully developed language, and some fall in the middle of these extremes.
Let's investigate the current state of knowledge, to find out what we really know about age and language acquisition.
1. Simultaneous early bilingual acquisition is different. Yes, babies who are consistently exposed to two (or more) languages with both high-quantity and high-quality input from birth can acquire these languages seemingly without effort. This natural form of bilingual acquisition happens all over the world in bilingual communities, where babies/children get an input flood of each of the languages. Replicating this type of bilingual acquisition in other circumstances is more difficult, and often less successful. Outside of bilingual communities, parents are often trying to pass on a lesser-used minority language, and exposing the children to the requisite quantity and quality of input isn't always easy. Parents who are hoping to have their children become bilingual from birth need to think about how they will ensure adequate input and build towards full competency.
2. Children aren't little sponges. If they were, all children would follow the same path/speed in language acquisition, and any parent with more than one bilingual child, and any educator with a class of language learners, knows that this is not the case. Children don't become fluent in a language just from hearing it for a few hours a week. It takes time, and effort. And there is only so much time and cognitive attention available in a normal day, so spreading it across multiple languages will have an effect. We know it takes children 3-7 years in full-time schooling to develop full academic proficiency. If we put children into bilingual programmes where they are learning two languages, it will take longer. If we want them to develop full academic fluency in the home language(s) as well, that will also take time and effort. Trying to push children into learning too many languages risks both their overall language development and their academic achievement - more isn't always better.
3. In research on (Canadian) immersion schools, the differences in ultimate attainment of children in early (from kindergarten), middle (from end of primary) and late (from secondary) immersion were minimal. The main significant difference is in accent - younger children have a better chance (but not a guarantee) of developing a more native-like accent. Other than that, the older children pick up the language more quickly, and in the end have similar proficiency - so the early start is not necessary. That doesn't mean an early start is always a bad thing; in fact for many reasons it works well. But it does mean that we don't need to try and fit in all the languages at the same time - we can and do develop fluency in languages we learn later, if we need them and are building on a strong foundation. And the bottom line is that strong foundation - anything we do that jeopardizes the continued development of their own language is not worth the potential consequences.
4. Adults can and do learn languages very successfully. In fact, the reasons why adults generally seem to have less success are often linked to time and focus, not to age. The reality is that as adults, we are busy. We have jobs, and families, and hobbies. Fitting in a language class is one thing, but finding the same amount of time to dedicate to it as young children can (no jobs!) is a challenge. So as adults, we make judgments on how much time and effort we have to expend on language learning, and it's usually just not enough to develop fluency. We also often perceive that adults are not good at learning languages because they tend to have accents, but an accent isn't a sign you aren't fluent in a language. It's just an artifact of your own language shining through. Or, as Trevor Noah wisely said: "An accent is just someone speaking your language with the rules of theirs."
So before we expect children to learn all the languages, take a step back and consider the time and effort of what they are already doing, and whether we really need to add another language right now?