I definitely didn't mean to say learning languages as an adult is easy because children do it. I've always thought methods like Rosetta Stone are complete crap because, as you say, we don't have thousands of hours to put into this like children do.
But what we do have is the most powerful tool we know for learning: language! Adults use their already acquired language to make learning a new language easier.
What I really meant, though, is there's nothing fundamentally "hard" about most things in everyday language. Being "hard" is quite hard (heh) to define but some things are intuitively hard, for example, playing Stravinsky's Petrouchka is always going to be considered a remarkable achievement for a piano player. But natural languages aren't like this. They are almost by definition easy because they are natural. If it was hard people would figure out an easier way to talk.
But what we do have is the most powerful tool we know for learning: language! Adults use their already acquired language to make learning a new language easier.
What I really meant, though, is there's nothing fundamentally "hard" about most things in everyday language. Being "hard" is quite hard (heh) to define but some things are intuitively hard, for example, playing Stravinsky's Petrouchka is always going to be considered a remarkable achievement for a piano player. But natural languages aren't like this. They are almost by definition easy because they are natural. If it was hard people would figure out an easier way to talk.