The present study reviewed research concerning young children's acquisition of English as a second language. The followings are suggestions obtained from the reviewed research. 1) Younger children are better able to learn phonology of a second language. 2) Phonological categories of the native language are still flexible in the early childhood. Young Japanese children are able to perceive English sounds in a CV structure correctly. 3) Young Japanese children are sensitive exclusively to the boundaries between morae, which makes it difficult to perceive English sounds in a VC structure or in multiple syllables. 4) Children's facility in phonological awareness of English is closely related with the acquisition of English vocabulary, and it is important for young Japanese children to facilitate phonological awareness of English. 5) In activities that require the manipulation of sounds of English words, Japanese children older than 5 years will be able to facilitate phonological awareness skills not only for English but also for Japanese.