While it's sort of true that children can learn a second language faster than an adult... It's actually a little bit more complicated than that, and also, the advantage children have is often widely overstated and is not actually as much as many people think it is.

It's true that brain plasticity is a part of it, but contextual/ circumstantial reasons are actually a huge reason why people end up believing children learn so much faster than adults.

When children, especially young children, are learning a language, they're typically immerged in a very full and complete way with a LOT of input, including many songs, games, TV shows etc that give a lot of basic vocab (numbers, colours, shapes, animals) to them in a very repetitive way, over and over again.

It's also often the only or main thing they're focusing or spending their time on. They're not trying to study while maintaining a job and all the other parts of their life.

If you take a family that moves, say, from America to France, and has a school age child, that child is going to be fully immersed in a French language environment (school) 5 days a week, and more if they do extra curriculars. It's going to be tough for an adult to have exposure to the same environment - if their job requires them to speak french they probably already speak it, and if it only requires a basic understanding, they're probably not getting anywhere near as much input and exposure as the school child.

If you look at the language level of a 5 year old child, and then imagine you've been learning a language for 5 years in a fully immersive environment, living in the country of that language, having lots of input every single day, and having lots of people helping you with learning it, it's not ridiculous to imagine you might achieve a similar level of ability.

It's also worth noting that especially with younger children, they're focusing entirely on speaking and listening and not even trying to do much in the way of reading yet. Can I speak better French than a 5 year old French kid? Almost certainly not right now. But can I *read* better French than a 5 year old French kid? I'm unsure. Maybe? But I think it would be difficult to assess as my strength would lie in different places. I might be able to read out a paragraph at a good speed but only understand half of it...

Part of my point is that adult learners often have (and need) a different approach which is going to cause learning to happen in different areas at different paces.

And also, that it can be easy to dismiss language learning as something "easy" for kids and too hard now we're "too old" without accounting for a lot of the reasons it's "easier" for kids (other reasons also including that young children in the early stages of language learning don't have embarrassment and fear of getting it wrong getting in the way so much).

I will note that children *do* have a much stronger advantage when it comes to the *sounds* of a language and the accent, and this part of it does get harder as an adult as we lose the ability to perceive sound differences that aren't important in the languages we already speak. You can retrain your ear and mouth but in many cases only so much (and it's a common experience for immersive adult learners to find their mouth muscles hurt when speaking a new language they're not yet used to).

But accent and fluency/proficiency are completely different things. In the same way someone can be equally proficient in English to me if they have an American or Australian accent as opposed to a British one, the same is true if someone has a French or Swedish accent. Unless the accent is *heavy* it's rarely a marker of how actually fluent/proficient someone is in a language and most people retain some amount of their natural native accent, whether it's from a different language, or simply a regional variety of the same language