When I was in school, the first verse went:

Sah ein Knab' ein Röslein stehn,
Röslein auf der Heiden,
War so jung und morgenschön,
Lief er schnell es nah zu sehn...

Notice the line 'war so jung und morgenschoen.' This line has been simplified to 'war so jung und war so schoen.' The original says that the rose was young and morning-beautiful. I think the idea 'morning-beautiful' deserves to be preserved.

I googled 'Johann Wolfgang von Goethe gedichte' and found a site in German which says that 'morgenschoen' is right.