Learning word order is one of the earliest feats infants accomplish during language acquisition [Brown, R. (1973). "A first language: The early stages", Cambridge, MA: Harvard University Press.]. Two theories have been proposed to account for this fact. Constructivist/lexicalist theories [Tomasello, M. (2000). Do young children have adult syntactic competence? "Cognition, 74(3)", 209-253.] argue that word order is learned separately for each lexical item or construction. Generativist theories [Chomsky, N. (1995). "The Minimalist Program." Cambridge, MA: MIT Press.], on the other hand, claim that word order is an abstract and general property, determined from the input independently of individual words. Here, we show that eight-month-old Japanese and Italian infants have opposite order preferences in an artificial grammar experiment, mirroring the opposite word orders of their respective native languages. This suggests that infants possess some representation of word order prelexically, arguing for the generativist view. We propose a frequency-based bootstrapping mechanism to account for our results, arguing that infants might build this representation by tracking the order of functors and content words, identified through their different frequency distributions. We investigate frequency and word order patterns in infant-directed Japanese and Italian corpora to support this claim. (Contains 4 figures and 1 table.)