The "red light district" is a fairly small area you can avoid with ease. Search for "De Wallen, Amsterdam" and it will pinpoint the neighborhood within which 95% of all adult filthy businesses are located (the southern part of De Wallen is not a red light district, but you can avoid it altogether).
As a suggestion, I'd take a tram from Amsterdam Centraal straight to Leidesenplein (trams #1, 2 or 5). From there I'd walk slowly my way back to the station walking through Joordan and Grachtengordel-West. That is a pleasant walk on a fair weather day.
If you don't want to bother with trams, you can just exit the station and wander on a Southwest/west direction, and you will reach these areas full of canals and old houses.