Previous studies on bilingual children found intact tonal development at the initial stages of interaction between Cantonese and English in successive bilingual children, whereas children exposed to both languages from birth have not been studied in this regard. We examined the production of Cantonese tones by five simultaneous bilingual children longitudinally at 2;0 and 2;6, and compared them with age-matched monolingual children using auditory analysis. Our results showed that some bilingual children had a delay at 2;0, compared to their monolingual peers. Some bilingual children also exhibited a 'high-low' template in their production, resembling the pitch pattern of English trochaic words. These findings suggest a possible early interaction of the Cantonese and English prosodic systems in which bilingual children adopted the English stress pattern in Cantonese production. The time-point along the trajectory of phonological development is important in modulating whether cross-linguistic transfer can be observed.