This sample is far too small to draw definitive conclusions about the differences in hair care between adoptive white parents and all black women (especially when I'm sure you also see black girls raised by black women without relaxers too).
I won't generalize, but the adoptive white parents that I have known or seen on youtube/internet seem to want to fully embrace the experience of having a "different" child. Also, (based on my experience) they are very aware of how they will be perceived if they try to straighten a black child's hair. Permanently straightening a black child's hair as a white parent is NOT politically correct. Again, not generalizing, but based on what I've seen, many seem to go hard to prove that they aren't trying to change their "different" child.
With all that said, most of the random compliments that I get about my natural hair (outside of black women) are from white men and women. Even my white friends have told me that they prefer my kinky/curly fro over my flatironed hair.
Gonna guess that it has more to do with lack of experience with black hair rather than them actually appreciating the hair, which is why you will often see a lot of those kids walking around with their hair all over the place.
Personally know/grew up with black chicks who grew up in white households. They are probably the most insecure when it comes to their hair and keep weaves on deck at all times as they get older. IMO, they turn out no different or better when it comes to black girls raised in black households.
The problems black women (and men) have with black women's hair extend far beyond a parent's realm. If that was the case, there'd still be a good portion of natural afro puff black women following their mothers from the 1970s.
Preach sir.