therefore, those children would be more white than anything else...
That depends on the individual.
in that respect it would not be fair to compare them to light skinned african americans who, for the most part, have <%50 european blood.
Many MG-mixed (multi generational) persons, in fact, have more than 50% European admixture. In particular, when we are referring to "light skinned blacks." And surely, because many "white" identified persons have recent African admixture, there are FG-mixed (first generation) persons who have more then 50% European admixture. Moreover, not all LSBs have less European admixture then do all FGM.
Keep in mind that nearly all "black" Americans have significant recent European ancestry, and many "white" Americans vice versa.
I have no problem with the idea that persons who identify as "BW biracial" have slightly more European admixture ON AVERAGE then do light skinned persons who identify as "black" (in other words, light skinned blacks), if that is true (I don't know if it is or isn't, and don't see much relevance to the point either way). But the idea that the social identity label that is called "B-W biracial Americans" has one particular admixture amount that defines it and that the social identity label that is called "light skinned blacks" has some other set admixture amount is ludicrous.
These social groups are not the same thing as admixture, plain and simple. They are not about phenotype either. They are not really even about biology in any meaningfully true sense, except insofar as appearances codify for the conventional application of certain social rules.