The study examines whether speakers exaggerate prosodic cues to syntactic structure when addressing young children. In four experiments, 72 mothers and 48 non-mothers addressed either real 2–4-year old or imaginary children as well as adult confederates using syntactically ambiguous sentences like Touch the cat with the spoon intending to convey either an instrument (high attachment) or a modifier (low attachment) interpretation. Mothers produced longer segments and pauses in child-directed speech (CDS) compared to adult-directed speech (ADS). However, in CDS, mothers lengthened post-nominal pauses in both the instrument and the modifier sentences to a similar extent thereby failing to disambiguate between the two interpretations. In contrast, non-mothers provided reliable prosodic disambiguation cues in CDS by producing post-nominal pauses that were longer in instrument than modifier sentences. Experiment 5, using ratings from 50 participants, determined that expressed positive affect was higher in the CDS of mothers than of non-mothers. Negative correlations between vocal affect and degree of prosodic disambiguation in CDS compared to ADS suggest that there may be a trade-off between affective and linguistic prosody such that greater dominance of affective prosody may limit the informativeness of prosodic cues as markers of syntactic structure.