The impact of foreign languages (mainly English) learning on children's language development has always been a hot issue in China. There is still no consensus on the idea whether the earlier children learn a foreign language, the better their language competence will be. Some scholars even worry about that early English language learning for Chinese young children will lead to a series of problems: the absence of mother tongue, the crisis of cultural identity, the lack of study motive, the lost of study desire, the increase of frustration, and the poor learning effect, etc. This paper studies the impact of foreign language learning on children's language competence from the five elements of metalinguistic awareness: phonological awareness, orthographic awareness, word awareness, syntactic awareness, and pragmatic awareness, including the promotion function, the interpretation mechanism, and the positive influence on basic language abilities, so as to find out the impact factors for foreign language learning and provide valuable reference for the establishment of foreign language educational policy and system in China.