Both, technically. Mixed races are still a valid member of both communities. However, not all mixed race kids prefer to specify both their races, if they don't feel particularly in touch with one community or another. I knew a hapa in an Asian community who felt more Japanese than white, and vice versa. I also know hapas that feel wholly they are both, and are comfortable with calling themselves hapa, and clarify upon further request.

Whatever they're comfortable labeling themselves, they'll refer to themselves as. It's always good to foster a sense of identity in botj communities though. A big issue is hapa children feeling a confused sense of identity because neither side validates their belonging enough.