There is little consensus among different early childhood education stakeholders in Hong Kong on whether it is beneficial or detrimental for children to receive an English bilingual education before the age of 6. This longitudinal study investigated the issue of potential "detrimental effects of learning English" on Hong Kong kindergarten children's performance in L1 (Cantonese) and L2 (English) over a six-month period. The sample consisted of 53 children, 29 of whom went to international schools and received 90 minutes of daily in-class English instruction, and 24 of whom went to local schools, and received 20 minutes of daily in-class English instruction. Analyses of the relationship between L1 and L2 development showed "no" evidence that learning a second language is detrimental to the learning of the first. This was despite the large difference in the amount of in-school instruction time the children who went to local vs. international schools received. Children in the international schools vastly outperformed those in the local schools in English. We found no evidence that learning a second language is detrimental to learning more general cognitive skills. The results provided very weak evidence for the opposite. Thus, learning English as a second language in Hong Kong before the age of 6 did not harm children's learning in any way.