You are confusing biological ethnicity with geographical nationality.
My kids are English, Mrs K is English, however ethnically they are according to the demographically tick box on atypical government based forms, English/Afro Caribbean. In reality they are English kids with a mixed race gene pool. When they grow up if they decide to refer to them selves as white, black, mixed race, English, West Indian, Caribbean or move to say, Australia and decide they are of Australian nationality is no skin off my nose*. One of them has a distinctly Welsh name (hopes AA doesn’t read this).
*unless one of them plays international rugby for Aus in a match that features a win over England, then Dads
Law applies.