English-speaking children make pronoun case errors producing utterances where accusative pronouns are used in nominative contexts ("me do it"). We investigate whether complex utterances in the input ("Let me do it") might explain the origin of these errors. Longitudinal naturalistic data from seventeen English-speaking two- to four-year-olds was searched for 1psg accusative-for-nominative case errors and for all 1psg preverbal pronominal contexts. Their caregivers' data was also searched for 1psg preverbal pronominal contexts. The data show that the children's proportional use of me-for-I errors correlated with their caregivers' proportional use of "me" in 1psg preverbal contexts. Furthermore, the verbs that children produced in me-error utterances appeared in complex sentences containing "me" in the input more often than verbs that did not appear in me-for-I errors in the children's speech. These findings are discussed in the context of current explanations for children's case marking errors.