In spoken Danish, matrix clauses with jeg tror (‘I believe/think’) follow a crosslinguistic pattern where matrix clauses indicating speaker belief are recurringly phonetically reduced to signal their background status. In such cases, speakers may diachronically stop recognizing the internal structure of the clauses which may then end up as unanalysed monomorphemic expressions. Research on English acquisition of matrix clauses with I think suggests that phonetic reduction in the ambient language conspires with deviant distribution to lead to morphosyntactic opacity for children. This paper presents an examination of all matrix clauses with jeg tror produced by 48 Danish children aged 1;9-6;7 in a 104-hour group-conversation corpus. Though the corpus counts at group level seem to comfirm the suspicion that the youngest children do not recognize the morphemic structure of the matrix clause, analysis at the level of the individual invalidates this oft-repeated claim. Further, comparing children and adults reveals that the oldest preschoolers reduce the expression far less than adults do, indicating active segmentation and not blind copying of sound strings.