This is a difficult comparison to make. When we say easier, I think we mean without conscious effort (e.g bilingual kids). How old were you when you would consider yourself fluent in your native language?
Suppose you compared an adult with five years of Spanish lessons versus a five year old bilingual Spanish speaker. Almost certainly the child will have better conversational fluency and will be better at aural comprehension, but the adult is likely to be able to express more complex things. For example I'd expect someone with 5 years of regular Spanish lessons to be able to mostly comprehend a newspaper, ignoring specific vocab. I'm not sure I'd expect the same of a 5 year old.
But now imagine an adult with 5 years of (buzzword) immersive language training. You move to the country, you speak every day (and ask people to correct you), you watch TV shows and listen to the radio, you read the newspapers. I think you could easily be comparably fluent to a 5 year old bilingual.
What you're saying is true - kids have the advantage of parents correcting them constantly, if they go to a school in their second language they'll have teachers and classmates correcting them. Though I'd argue that hanging around kids will only make you as good as those kids. That is, you will become very fluent using the language simply (which is probably the hardest to learn as an adult), but it will still take years to know concepts that adults already know and can transfer.
I suggest that anyone who thinks a child has an easy time learning a language should try to explain a foreign concept (which all language is, initially) to a 4 year old.
https://www.jstor.org/stable/1128751 https://journals.sagepub.com/doi/abs/10.1111/1467-9280.01415
Basically there's a relationship between time invested and skill that's nearly the same no matter how old you are (and perhaps even in the adult's favor). But what DOES differ significantly is that adults typically don't spend 8-16 hours every day immersed in their target language.
> 2. No one will put up with your shitty language skills for more than 5 minutes... Except your significant other. They'll have the patience because they love you. Everyone else will just cringe after a few minutes and change to English, or just smile and wave you off.
I suspect these two put together are actually the reason why it's easier to learn languages as a child.
I'm not familiar with the evidence (how could you test this?) but it seems to me that everyone I go as an adult people will switch to English as soon as they hear I don't speak the local language.
As a child, it's different. You're constantly corrected, and people will forgive your mistakes indefinitely. Also you're hanging out with kids, and they tend to only speak one language, so you end up learning it from them.