Early bilinguals-those exposed to their second language (L2) during early childhood or who grew up bilingually from birth-are regarded as bilingual first language acquisition (BFLA) children. This paper investigates the production of word-initial Japanese stops by Japanese-Mandarin BFLA children growing up in southern Taiwan. Examination of Japanese word stop voice onset times (VOTs) by these bilingual children, aged 3-6 years old, revealed three important findings: (1) They tended to replace Japanese voiceless stops with Mandarin aspirated stops as well as Japanese voiced stops (except voiced stops with negative value) with Mandarin unaspirated stops; (2) Some children as young as three years old were able to produce prevoicing in Japanese voiced stops; and (3) Error patterns including aspiration and devoicing also suggest that they have established a unique phonetic system, the result of a mixture of both languages.