"Das Kind lernt schnell."
Translation:The child learns fast.
I entered quickly and it was accepted. Although both quick and fast would be understood in english.
frozenflames9 - You've probably read or heard that silly comment that goes something along the lines of:
"Deutsche Sprache, schwere Sprache."
I'm sorry but, I think the word "Deutsche" should be replaced with "Englische", because this is one of the many examples in which German is quite clearly easier to explain.
The adverb "quickly" would definitely work in this case, but so would the adverb "fast", because "fastly" doesn't even exist. It's one of those adjectives that doesn't go through the usual addition of the "-ly" suffix process in order to become an adverb. There's several of these adjectives out there.