Translation:The child is not fast when it runs.
The sentence is wrong. You can't say "hurtigt" in this sentence. It would be the same as saying "quick" and "quickly" is the same word. But as you know, it isn't; here are some examples:
He is fast/quick=Han er hurtig. he runs fast/quickly=han løber hurtigt
This is because quick is an adjective and quickly is an adverb but it's easy to mess up since you can use fast in both contexts. c;