"It takes many adults to be able to defeat a magic creature"
This is a world that doesn't have the word "magic". He didn't recognize the word or concept earlier. Perhaps some other kind of word would be better for him to use to describe such unnatural creatures as fairies, goblins, etc., as distinct from normal things like fish and cows, etc. For that matter, we know that fish are magical in some ways, but they are not regarded as monsters because most people cannot see the magic manifesting from them.