This study investigated VOT of word-initial Japanese and Mandarin stops produced by Mandarin-Japanese bilingual children in order to observe bilinguals’ phonetic systems. Examination of Japanese and Mandarin stop productions at the same articulation points in bilingual children aged three to six years old revealed important findings: (i) They tended to lengthen VOT values at the age of four and five in Japanese stop production, and at the age of five in Mandarin; and (ii) They maintained phonetic contrast in three VOT categories in their two languages: a) voiced stops in Japanese/unaspirated stops in Mandarin, b) voiceless stops in Japanese, and c) aspirated stops in Mandarin. These VOT patterns lend credibility to the idea that early bilingual children develop distinct Japanese and Mandarin phonetic systems, while showing cross-linguistic influence in each language. The findings of this study could provide a better understanding of the phonological representation in early bilinguals.