we've avoided this whole discussion with our kids out of sheer terror of teaching them the "wrong" usage, and they simply refer to some people as having dark skin and some people having light skin.
typical example:
Kid 1:Which teacher is Ms. Smith?
Kid 2: She's a 6th grade teacher, you know her, she's sort of heavy? has dark skin?
Kid 1: Oh yeah.
...
Kid 2: She's a 6th grade teacher, you know her, she's sort of heavy? has dark skin?
Kid 1: Oh you mean the one that more melanin than I do?
...
us 'white' people are malanin-challenged. mutations actually.