The number of children living in the United States who are learning two languages is increasing greatly. However, relatively little research has been conducted on the language and literacy development of dual language learners (DLLs), particularly during the early childhood years. To summarize the extant literature and guide future research, a critical analysis of the literature was conducted. A search of major databases for studies on young typically developing DLLs between 2000 and 2011 yielded 182 peer-reviewed articles. Findings about DLL children's developmental trajectories in the various areas of language and literacy are presented. Much of these findings should be considered preliminary, because there were few areas where multiple studies were conducted. Conclusions were reached when sufficient evidence existed in a particular area. First, the research shows that DLLs have two separate language systems early in life. Second, differences in some areas of language development, such as vocabulary, appear to exist among DLLs depending on when they were first exposed to their second language. Third, DLLs' language and literacy development may differ from that of monolinguals, although DLLs appear to catch up overtime. Fourth, little is known about factors that influence DLLs' development, although the amount of language exposure to and usage of DLLs' two languages appears to play key roles. Methodological issues are addressed, and directions for future research are discussed. (author abstract)