I used to be very sensitive about this issue, too, as both my DC (also mixed white/black Carib) always got comments.
I got comments about my DS because I allowed his hair to grow into a big unruly afro ('why dont you braid it/cut it/ oil it?' etc etc...um, because he is little and his natural hair is beautiful and doesn't need messing with!...funnily enough he is now approaching teenage hood and likes it skinned right off in a very low fade, so glad we had those years of him with all his lovely hair
).
My DD also got comments (or rather, I did...because of course, her father has nothing to do with it
) because I don't plait her hair beyond two simple braids, and mostly she wears it in simple ponytails or buns (I can plait hair, but her hair is not afro texture, its tightly curly but fragile and it doesn't respond well to tight braiding at all).
My take on it is this: Hair is a big thing in some parts of the black community. Pride in how you take care of your hair/your DCs hair is important. And I think there is a perception by some black people that some white mothers are lazy/ignorant and don't bother to learn how to look after their mixed race DC's hair. But if you know thats bollocks where you are concerned, I would honestly just ignore, ignore, ignore and dont let other people project their assumptions and issues on to you and your DC.
Funnily enough, I dont take advice from anyone other than mixed race people or other parents of mixed race children on mixed race hair issues, because in my experience, both black and white hair people can be generally pretty rubbish with many mixed hair textures. White stylists are scared to cut it, black stylists want to weigh it down with heavy products or braid it so tightly the hairline breaks. No thanks!