Purpose The purpose of this study was to examine the independent and combined contributions of fundamental frequency (F0) and vocal tract length (VTL) differences on children's speech-in-speech recognition in the presence of a competing two-talker masker. Method Participants were 64 children (5-17 years old) and 25 adults (18-39 years old). Sentence recognition thresholds were measured in a two-talker masker. Target sentences had either the same mean F0 and VTL of the masker or were digitally altered so that the target and masker differed in F0 (Experiment 1), differed in VTL (Experiment 2), or differed in both F0 and VTL (Experiment 3). To determine the benefit, masking release was computed by subtracting thresholds in each shifted condition from the threshold in the unshifted condition. Results Results demonstrate that children's ability to benefit from either F0 or VTL differences (Experiments 1 and 2) depended on listener age, with younger children showing less improvement in speech reception thresholds compared to older children and adults. Age effects were also evident in the combined-cue conditions (Experiment 3), but children showed greater improvements compared to F0-only or VTL-only manipulations. Conclusions There was a prolonged pattern of development in children's ability to benefit from F0 or VTL differences between target and masker speech. Young children failed to capitalize on F0 and VTL differences to the same extent as older children and adults but did show a robust benefit when the cues were combined, supporting the hypothesis that younger children rely more heavily on redundant cues compared to older children and adults.