This is a comparative study that explores preschoolers' English vocabulary acquisition in Taiwan and tries to look for a better pedagogy. After Taiwan's government announced the policy of developing a "Bilingual Nation," English is the second language in Taiwan. The reforming of English instruction is in urgent need. Under this background, this research aims to investigate whether English vocabulary acquisition will occur in a variety of GBL. In this study, we grouped participants into four instructional groups. Two groups are designed as instructional groups of "flashcard game" in learning 2 words or 3 words per day. Another two groups are designed as groups of "driving games" in learning 2 words or 3 words per day. Without explicit instruction, the study's result showed that preschoolers' English vocabulary acquisition can occur autonomously by GBL, and "2 words per day" is the best and suitable vocabulary size for preschoolers to acquire English in their memory. We found that games can produce children's autonomous learning, and the numbers of children's vocabulary memory can be taken into consideration. Besides, the appropriate amount of information can train children to enter long-term memory. The above findings will benefit language learning, game-based learning (GBL), and interactive learning.