Subject-auxiliary inversion in interrogatives has been a topic of great interest in language acquisition research, and has often been held up as evidence for the structure-dependence of grammar. Usage-based and nativist approaches posit different representations and processes underlying children’s question formation and therefore predict different causes for these errors. Here, we explore the question of whether input statistics predict children’s spontaneous non-inversion errors with wh- questions. In contrast to previous studies, we look at properties of the non-inverted, errorful forms of questions. Through a series of corpus analyses, we show that the frequency of uninverted subsequences (e.g., “she is going” in “what she is going to do?*”) is a good predictor of children’s errors, consistent with recent evidence for multiword units in children’s comprehension and production. This finding has implications for the types of mental representations and cognitive processes researchers ascribe to children acquiring a first language.